Will a 7900GTX work with a 8400GS (as secondary) in Vista 64bit?

Ok I have been looking around the net and can't find an answer, hope you guys (and gals ;-) can help.

I have a 7900GTX and I want to have four monitors so I need to add a second graphics card, I was thinking of a 8400GS (since it supports CUDA and I do a lot of science crunching). Will the following setup work? ( I want to know before I buy the 8400GS)

1) 7900GTX as primary card and 8400GS as secondary under Vista 64bit. ?

Current system:
Dual Quad core XEONs overclocked to 2.33GHz (custom liquid cooling setup for quiet operation)
Seimens-Fujitsu montherboard with one 16X and one 8X PCI Express slots (both are 16x size but one runs at 8x)
8Gig Ram in Quad channel
Vista Ultimate 64bit
850 Antec EPS 12v Power supply

If the nVidia setup won't work I also have a ATI 1900XT and a 2650 Pro(not sure if I got that right, been a while since I used them)

Thanks

Cheers

John

oops I don't think I mentioned the reason why I want to do this, I want to run 4 monitors in total and while I would like to, and plan on upgrading the 7900GTX to 260GTX or better, I NEED 4 monitor outs and need Vista to recognize it.

Hope this helps.