suposedly this intel 845 video card can take up to 64 mbs of ram but intel does this when it need to do it, it doesn't take all the time the whole 64 mbs of ram, it can take 11, 6, 30 or whatever it wants and that is a serious problem for games in windows and in linux as you see not all the time this works as expected
some bios can force to use a determined amount of ram for video but mostly this is done automatically by bios and video card
it takes a certain amount of ram from each ram module available, also depends on how big the ram module is, if you can try adding at least 512 mbs more so the system can take at least 32 mbs all the time