Question on MSI P7N 750i Platinum

I was wondering if I had 2 x 9600gt in 8x sli-mode, would I be able to use the other 16x pci-e slot for an additional card(like an old 7300gt I have?)

Probably not

If the bios will support it...I remember that win98 would allow for 9? video cards that you could use as one huge desktop, or have a different window opened on each display, and you could drag n drop between..don't know if they removed this feature in the later OS's.
I found an article here: http://support.microsoft.com/kb/307873/EN-US/
Hope this helps,
Doc