Firstly, a 1GB graphics card doesn't use up main RAM. It has its own RAM on board.
The problem for people with 32 bit OS is that a 32 bit CPU can only address 4GB, so with 2GB ram + 1GB graphics there isn't much left for stuff like the BIOS and any tricks the operating system might want to pull with addressing to speed things up.
64 bit OS removes that (for now
), I make 2^64 locations roughly 18 million terabytes.
As that is a bit big, Intel don't bother bringing that many address pins out on their chipsets and currently limit the implementation to somewhat less. Still, I think you get the point that the OS should find somewhere to put it
