Vista is your answer. use Driver Cleaner to remove the drivers , then reinstall them again..  ... www.guru3d.com

I have dual 7900GTX cards on an SLI config in my XPS 700.

I was able to turn on SLI by installing the nVidia BETA driver, version 101.41.

Found here:

http://www.nvidia.com/object/vista_driver_news_030207.html

 

It works perfect for me.  Tested it on games like Ghost Recon Advanced Warfighter, Battelfield 2, Oblivion, and S.T.A.L.K.E.R. and they look fantastic.

 

Ok, so I used driver cleaner, then tried to install the beta driver (101.41) and my rig crashed, I tried again and it crashed again. I used driver cleaner again and was able to get the last release driver installed but again no SLI mode :(. Dell support won't help me since I upgraded to Vista, and my service plan doesn't expire until 2010 :(

You may want to take a look at http://www.nvidia.com/object/ntune_5.05.25.00.html, I have used it to restore the "Perfomance" section of the Nvidia Control Panel.

 

-Patrick

XPS L2 Tech PHX

If you wanted to try the BETA driver again:

 

Try right clicking on the driver update and click Run as Administrator.

As far as it "just restarting", the same thing happened to me.

I was able to successfully install the driver.   However, when I tried to apply SLI, I was given a notification that for SLI to be enabled, some programs had to be closed.  At that point, I could only click OK.  Then my resolution got forced to 800x600.  Then I got a window telling me that the system needed to restart.   The first time, I clicked ok to the restart and I found that SLI did not work.  The second time, I clicked Cancel.  I got that restart message a few more times and clicked Cancel each time.   Finally, I got a message that told me that for the changes to take affect, the system must be restarted and all I had was an OK button.  So I clicked OK and the system rebooted.   Once back at the desktop, my res was still at 800x600.  So I changed that to the res I like and then when to the nVidia Control Panel and was able to successfully turn on SLI.

 

nVidia said they were hoping to have an SLI compatible driver out by the end of March.  I guess they aren't done with it yet.  But it should be released soon.  If you go with the current official driver (version 100.xx), that will give you the options to do screen rotation, but no SLI yet.  

When you say you tried to install the Beta driver and the system crashed... what exactly happened?

Bingo.  It's all up to nVidia to make a Vista SLI capable driver.

This is from the release notes of the current official release (ver 100.xx)