Have a read of this

http://www.w7forums.com/windows-7-64...-bit-t484.html

Its been a while since I did binary maths, but maximum address space wth a 32 bit number is 4GB as far as I can recall.

AGP graphics cards can be separate, but they do still use some shared memory. Lots of laptops do this nowadays. Use something like Belarc Advisor and it will show you the amount of dedicated video RAM and the shared video RAM taken from main memory.