hanging up and stalling

yes if you have a faulty slave this will impair the running of the master drive,
Do you have three hdd on this pc?
Sounds to me that your processor cannot handel that 300 gig hdd as well the two., how many partitions do you have on that 300 gig? Or any of therse hdd. If I remember somewhere there was a write up about problems xp experiences running large hdd.
EXTRACT>>  please read on from what I pasted here to grab your interest :)
http://www.pcbuyerbeware.co.uk/IDE1.htm
The Cap Limit setting automatically sets the drive to a system's maximum size capacity, because many systems cannot run huge drives. This particular DiamondMax Plus drive (5400RPM, 2MB cache, 12.6ms disk access time), has a capacity of 300GB that unmodified Windows 9.x systems, which run the FAT16 or FAT 32 file systems, won't be able to run as a single (unpartitioned) volume. Windows XP, running its NTFS file system, can run such a drive if the motherboard's BIOS setup program allows it. If the BIOS doesn't allow it, reflashing it with the latest BIOS file from the PC manufacturer or motherboard manufacturer's site might fix the problem. Otherwise, installing a new PCI IDE adapter card of the kind made by Promise, or a new motherboard that has a BIOS capable to recognising such a large HDD is the only remedy.

The easiest way to configure and install an IDE ATA 66/100/133 HDD, which has to be installed using an 80-conductor ribbon cable (not an old-style 40-conductor cable), is to set the drive's jumpers to the Cable Select setting. When jumpered for Cable Select, the cable plus the jumpering determines which is the master drive and which is the slave drive. The master drive will go to the black connector on the 80-conductor ribbon cable, and if a slave is used, it will be connected at the ribbon's middle (grey) connector. The ribbon's blue connector fits to the motherboard. As long as two HDDs are jumpered to the Cable Select setting, you can swap them from the master to slave positions on the ribbon cable.
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Hard disk may become corrupted when entering standby or hibernation or when writing a memory dump
http://support.microsoft.com/?kbid=331958
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This next artical is members only and I have learnt from past cannot give you this web link, it will not display for unless you login, so I have pasted the contents instead as I am a member>> sorry for the lenghty of it.
What's the problem?
If you have or support systems with ATA hard drive sizes exceeding 137 GB running any version of Windows XP or XP with Service Pack 1—Home, Professional, Media Center Edition, Tablet PC Edition, or 64-bit Edition—you may be at risk from a flaw in the operating system. This flaw may become apparent when the system enters Hibernation/Standby mode or after a memory dump is written out to the disk.

It's important to note that you aren't likely to run into this problem in XP without SP1, because only SP1 has native support for drives exceeding the 137-GB limit. While support can be enabled in pre-SP1 XP installations, this isn't recommended outside a test lab.

Only ATA drives are affected by this flaw. If you're running systems exclusively with SCSI drives, you aren't at risk.

Problem description
To make use of the space beyond the old 137-GB limit, Windows XP SP1 uses 48-bit logical block addressing (LBA). Unfortunately, the processes that write the memory dump and Hibernation/Standby files do not write their data to the disk using 48-bit LBA. Moreover, when a Windows XP SP1 system with 48-bit LBA enabled enters Hibernation, Windows fails to issue a flush cache command to the IDE system's cache. As a result, any information still in the cache won't be written to the disk.

There are a number of symptoms that you can watch for to determine whether you're suffering from this flaw. If your system restarts rather than waking up from Hibernation, or if you experience data corruption upon entering Hibernation/Standby mode or after a memory dump or stop error, you may be afflicted. Data corruption can manifest itself in a variety of ways including problems starting the system, shutting down the system, running programs, or opening and/or saving files.

The fix
On January 22, 2003, Microsoft issued two fixes for this flaw. The first fix supports the Home, Professional, Media Center, and Tablet PC Editions—all 32-bit editions—of Windows XP, while the second one is intended for the 64-bit 2002 Edition of Windows XP.

To obtain the patch for the 32-bit editions of Windows XP, download it from Microsoft's Web site. There is a different patch for the 64-bit 2002 edition of Windows XP that you can download and install separately. These are links to the English language versions of the patches. If you need a patch for a different language, follow the link and select the appropriate language from the selection box on the right-hand side of the screen.

Note also that this patch should be included in Windows XP Service Pack 2 which is—as of this writing—undergoing testing. The patch replaces a single file, Atapi.sys.

Installation
To install the fix, download the appropriate version of the patch and run the single downloaded executable. The patch installer will automatically create a system restore point that you can back down to in the event that the new driver causes a problem. After the installation is complete, restart the system.

Fix for frustrating flaws
Data corruption flaws can be among the most frustrating flaws to stumble across and recover from. If you're supporting systems that meet the qualifications for this flaw, I recommend that you proactively install the fix rather than risk encountering this problem.
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Check your event viewer from control panel administrative tools> event viewer> applications. There maybe some errors listed that may help point you in a direction of what the problem is.
Have a look in your system information and see if there is any problem devices.
Have you defragged at all? run chkdsk recently?