What type of disk controller?
When you say 'Disk-intense activity', what do you mean?  
How is your recycle bin?  If that gets full, the process of selecting files to permanently delete when delete other files can slow you to a crawl if you have a lot of files in the recycle bin.

It's an SATA drive.  Disk-intensive activity means anything that requires a lot of disk reads. The startup process and application startup are prime examples, but sometimes it can take about 20-30 seconds just to open a folder in Explorer.

Recycle Bin only had about five files in it, about 3-4 MB total.

Defrag your hard drive. OEM installations of Windows typically come fragmented because the disk image they use is fragmented. Also, removing a lot of unecessary utilities installed by HP helps by reducing the number of startup apps and freeing up memory.

The one thing that really help is disabling System Restore. You should invest in Norton Ghost and use that to make regular backups, then disable System Restore.

A far as the defrag goes:
if your download an evaluation copy of Diskkeeper
http://www.diskeeper.com/downloads/downloads-r.asp
You can get an idea of whether your drive is fragmented.  The Windows defragger (a license from Diskeeper for their Diskeeper Lite?) does do a report on actual file fragmentation, and I do not think it is as complete as Diskeeper full versions.
You say a lot of reads.  Are you also doing a lot of writes?

Try O&O Defrag. I have used it and it is the best I have come accross thus far. Get the trial here:

http://www2.oo-software.com/files/oodefragv8/OODefrag8ProfessionalEnu.exe

Alternatively, if you don't want to go through a lot of effort, the defrag utility that comes with Windows will get rid of install time fragmentation just fine, although for your regular defragmentation you will want to get a third-party app.

Please remember the pointers about System Restore and unecessary software; both take a lot of hdd space and read/write from the hdd thereby increasing unucessary i/o activity and reducing i/o capacity of the drive available to more deserving apps.

PLEASE PLEASE PLEASE get rid of any software you don't really use that came with the PC, especially those HP bundles etc. Just nuking those will make your pc noticeably faster and more responsive. I don't know why but OEM's love to install all sorts of supossedly useful apps that just choke most machines and turn what should be a fast computer into a slow bloated machine whose performance leaves you wandering why you bought it.

Hi guys, thanks for the tips...as I said above, I've tried defragging the drive, several times in fact, even when there was not much fragmentation to begin with.  I've removed quite a bit of the bundled software in favor of my own before it started to act up.

In fact, I'm actually writing this comment in Safe Mode and it was still slow starting up.  The drivers that load in text mode are loading really slowly.

One thing I noticed is that the drive controller in Device Manager shows Current Transfer Mode in "PIO mode", but the drop-down list says "DMA if available", and my BIOS shows my drive as UDMA 5.  For some reason it's throttling back to PIO; if I could only find out why...

My paging file size is 1524MB-3048MB.

And I might have to invest in Norton Ghost anyway, if only to backup the data before the drive blows up completely, if it is in fact the drive...

I'll run a chkdsk /r and let you know the results.

Found this.
http://forums.windrivers.com/showthread.php?t=62674
Check last comment on thread.

1. Go into the BIOS and make sure the ide controller is NOT in RAID mode. It should be native SATA

BACKUP your system BEFORE doing this:
Try reinstall the IDE drivers for the controller by going into device manager, uninstalling all IDE controllers and channels, then reboot. Windows should then automatically install the relevant drivers.
If Windows does not have the drivers for your ide controller by default, then yu will get a BSOD and have to retore your backup.

if you have copied a folder that has tons of files in it, the computer will slow down. i once copied all the cliparts from xp media content to the hard drive (about 10,000 pics). every time i opened up "My Computer", the computer read the file directory of all those files before it did anything else.
also, a virus or keylogger or monitoring software will slow a computer down. do a virus scan and check what runs when your computer starts.

set your drive to Dma mode, xp resets it when it has trouble accessing a drive (cd, disk).
You can try another sata port, or cable.
And you could try testing your harddisk, but this will need a complete reinstall, so image this one first.

http://www.disk-utility.com/hard-disk-low-level-format.html

Sorry for the delay in getting back...things took a turn for the worse yesterday.  Yesterday morning we had trouble booting up now.  Windows had trouble finding WINDOWS/SYSTEM32/CONFIG/SYSTEM and said I had to repair the file.  However, I was able to boot in normally on the 3rd try (big sigh of relief).

I've got Norton Ghost 10.0 installed and picked up an external HD, so I'm preparing for the worst, hoping for the best.  Right now my computer is STILL crunching through a chkdsk /r; the last I saw (about 2 hrs. ago) it was on 22% verifying the free space (which kinda doesn't surprise me given it's a 250GB drive with 200GB still free, but still...).  I started it about 4:30 p.m. HST yesterday, so it's been running about 16 hours.  No error messages were reported on the file data.

Before that happened, though, I uninstalled the Primary IDE Channel and let Windows reinstall and that reset the PIO issue, so it helped performance a little bit.

Will also run a full Norton virus scan at earliest opportunity, but the last full scan was back on 10/31/05 if I remember correctly (the computer was slow then too) and it didn't uncover anything so I doubt it will now...

Jerry: to address your earlier question about reads vs. writes, writes seem to be OK.  I was able to install Ghost on my HD with no significant performance issues.  And downloads seem to go smoothly.

Sounds like fun.
I asked my techs and got the info on our problems with SATA. Ours were on a Dell 670swith W2K Pro installed, if that matters.
We started noticing disk read errors, drives dropping from view, slow processing, etc shortly after deploying 4 like systems.
There were two possible issues: a.  Controller firmware and possibly the FAT-32 to NTFS conversion for the SATA drives.
We ended up flashing the chipset with the latest BIOS, the controller, and then reloading OS.  Didn't have a problem after that.
Fortunately, this all happoened
a.  Before we started using the systems for mission-critical data
b.  While we could get Dell to tell us they had controller problems with the systems in question.

OK, now I have to ask, is it normal for a 250GB to take close to 48 hours to complete a chkdsk /r?  When I left the house this morning it was only at 67% checking free space.

I would not think so.

Well, it looks like the disk may be toast.  The chkdsk /r **finally** finished at about 4:00 a.m. this morning (after 3.5 days!), and then it wouldn't boot up on restart..."Windows could not start because XXXX is missing or corrupted."  Got on the phone with HP tech support; the computer won't boot up in safe mode either.  And I can't even do a "destructive recovery."  Gotta wait for the recovery discs to come in from HP (the discs I should have made myself earlier).

On the bright side, at least the machine is still under warranty, so the replacement parts, if any, won't cost anything.  

Thanks for all the help thus far.  

Getting a new HDD too?
Ask them if there are any updates to controller and chip firmware.

Checked the HP site and there is a BIOS update, but the installation is Windows-based, which means I have to have a computer that's at the very least in a bootable state.  :(

Fortunately, the discs went out via FedEx Next Day so they should reach me by tomorrow afternoon.

No new disk yet...I guess they want to see if reformatting and reimaging the drive solves the problem before they pronounce the HD dead...personally, I'm not that optimistic, but we'll see.

It's official, the HD is terminal.  Tried the full system recovery after the CDs came in and it was still going at it after 10 hours, with each successive restart taking much longer than the last.  Finally, I just took it to CompUSA.  The tech just called me with the bad news.

The only good news is that it'll cost me nothing out of pocket.  (They did charge me $119 up front for the diagnostic but since HP's warranty covers parts/labor that will be refunded, he said.)  And it might be done later this week if they have an equivalent drive on the floor.

Thanks a lot for all the help, jerry.

Thanks.  Glad to help.  Thought others provided good input though.  Might want to split ponts.  Your call.