Vista Ultimate keeps rebooting

can you start in safe mode? any mini.dmp's? if yes post it here. vhange the extension to .txt from .dmp

Did you install anything recently? Drivers...updates....hardware? Make sure that your system isn't overheating...you'll might want to open your side case to your computer with the power off...and spray out any dust that is inside...using a aircan.

This is often a memory-related issue.    Vista uses your memory more aggressively than XP, so you may have a failure mode that's impacting Vista, but not XP (or perhaps XP isn't using the defective area).

To check for that, download the latest MemTest86+ ISO [http://www.memtest.org/ ], create a bootable CD, and boot to MemTest.     Let it run for at least an hour -- if it has errors, that's the issue.

If not, then you most likely have a corrupted driver.   The most common one that would cause the symptoms you're seeing is the video driver.    Try booting to VGA mode -- press F8 at the start of the boot process, then select "Enable low resolution video".     If that works okay, then uninstall the video driver;  download the most current driver for your system;  and then install it.

I did forget to mention that when I first powered it on after lunch today, it did say that it was installing update 3 of 3 - 0% complete, please do not turn off your computer.  

So I wait a moment and my laptop automatically reboots, but the next time it doesn't even get to that screen and reboots again.

It was probably not installing "update 3 of 3" -- it was probably installing updates and was at "stage 3 of 3".    But in any event, it seems to have either failed while installing updates;  or installed a corrupted update.

Try to boot to the "last known good configuration" ==>  press F8 at the start of the boot process and select that from the available choices [the same place I told you to try the "low resolution video" boot].

... you indicated this happened "... when I first powered it on after lunch today ..." ==> which indicates it was turned off.     You may have turned off the machine at an inopportune time while it was installing updates ... if so, the updates got corrupted, and that would explain what's happening.    Booting to "last known good" and then running Windows Update to redo the updates will likely resolve this if that's the case.

Thanks for all the feedback thus far, much appreciated!
Here's what I've tried.
Accessed the F8 Safe mode screen, I've tried, and in this order,
1. Last Known good configuration....  This again caused a reboot after the "Configuring update, Stage 3 of 3 - 0% complete, screen.
2. Disabled auto restart on system failure... Behaved the same as the first try.
3. Safe mode - Caused a blue screen of death with the following information.
   Driver IRQL NOT Less or Equal
   Stop 0x00000001 (0x00000A10, 0x00000002, 0x00000001, 0x8B61428A)
    iastorv.sys - Address 8B61428A base at 8B60C000  Date stamp 46fd4537
Collecting data for crash dump
Physical memory dump failed with status 0xC0000010

Hope all this helps, Thanks

Forgot to mention one stop I tried in between steps 2 and 3
On the safe mode screen was a restor or "system repair" item or something like that which only caused a reboot anyway.
Now I'm not sure if I tried this before or right after plain "Safe mode".
I just remember I got the blue screen last.

Sounds suspiciously like memory, as I noted before.     Create a bootable MemTest86+ CD (on another PC) and boot with it.    It will run the test automatically --- as I noted before, run it for at least an hour.

Or you can use the built-in memory test of Vista.  When you boot from the Vista DVD, that is one of the options presented in the Windows Recovery Environment:

http://www.bleepingcomputer.com/tutorials/tutorial146.html
How to Use the Vista Memory Diagnostic Tool

I ran memtest86+ 2.11 for an hour and a half.  No errors appeared on screen.

I then attempted to boot into F8 Safe mode - "Low resolution display 800x640".  Boot process again got to the Configuring update 3 of 3 - 0% complete, and the laptop reboot.

Looks like I may have to do a fourth reinstall in less than a month.
Any more ideas?  This is my business laptop too.

I have Vista Ultimate 32-bit running dual boot with XP-Pro on a 250GB SATA drive.  I'm typing in the XP side now.
The boot process defaults to Vista, but I have 30 seconds to decide if I want to continue there (and just hit enter) or decide to boot into XP.  I also have the option to hit the F8 key here to enter into "Safe Mode" where I can select and have tried: "Enable low-resolution video (640x480)" (I mistyped it above) or "Last know good configuration (Advanced)"  or "Directory Services Restore Mode"  or Disable automatic restart on system failure".  None of these have gone past the Config updates..... screen.
As far as reinstalling the system an creating an image, that's a whole other learning process for me.
I'm calling it a night for this evening and will resume further research in the morning.
Thanks again,
Lucy

IRQL issues are caused by poorly writen drivers.
Try to press F8 during boot then select last known good configuration. It should load your last working set of drivers.

Thanks garycase for your assistance.  I did have to re-install from scratch and as I'm still under warranty, I called Dell again.  This time I got a technician that walked me through installing the Dell ControlPoint software for these new Latitude laptops.  Previous Dell techs did not even mention it causing my laptop to crash repeatedly.
You help was much appreciated!