Oh and in case it makes a difference im using vista business 32 bit
I assume you have a good reason for it. Because it's 32-bit, your system will only see about 3.5 GB with an 8800GT. With two of them, probably 2.75GB to 3.25GB, I don't know. Try to get a 64-bit OS at some point.
Edit: I wanted to mention the HD 4850 too, but then I saw your SLI motherboard. Nah, you're better off with two 8800GT than with a single HD 4850. The HD 4850 can give you more performance than one 8800GT but you can't add a second card later if you go that way.
Make sure you choose a PSU that supports two 8800GT cards. There's a PC Power & Cooling 610W for $80 at newegg for example, or a 650TX for $90.