I use windows 7 ultimate 64 with 4GB of RAM 8 months ago and it ran fine with MOH 2010 and BFBC2... now I have 8GB of RAM because they are so cheap...
Graphics card don't map their entire memory into PCI space. My 1G video card only maps 256M, and I think that's typical. BIOSes can make that worse by address rounding and allocated more space than the card actually needs.
With a single PCI-Express card the amount of memory lost typically ends up being 0.5G or 0.75G.
Typically?
Yes, typically. That's why I used the word. It doesn't mean "always".
Well, except it's wrong.
Video cards actually do "typically" map their entire memory within the first 4GB, taking the place of normal usable memory.