Your video card and Windows Vista are designed to share system RAM, but only
when you need to do so. For instance, if you are running an application
(such as a graphics intensive game) that requires more memory than that which
is available on your video card, the system kicks in to allow it to use
general computer RAM. However, when your graphics usage has no need for
system RAM, it's available for other uses. It's a very good technology.

I have Vista Ultimate 32bit and it's sharing a comparable of system memory
for video support that equals the same amount of memory that my GPU a 8800GTX
has which is 768MB of ram.  How do I stop Vista from using 768MBs of my 2GB
installed system memory?