its because you have a 32 bit operating system. the max (there are convoluted ways around this) is 4GB. You then subtract everything else in the system that has memory that the OS needs to address (like your video card). Whatever room is left, goes to the RAM, which is usually between 2.5-3.5GB, hence, you only see 2.5GB. It sucks, but at least nothing is broken.
Do you have SLId 512MB video cards or something? That'd probably be the biggest draw on addresses.
I think anything that works on vista 32bit should work on 64 but I'm not positive. If you are considering switching to 64bit check that all your software will still work.
u should upgrade to XP much better for gaming all games play smother on XPWould it be worth it to upgrade to the 64 bit version? I use the system for gaming mostly. Is there any Microsoft program that allows you to upgrade to 64 bit from the 32 bit version?
As long as you have that much video RAM needing addressing a 32bit OS it going to run out of addresses before you get 3GB of RAM.I have two 6800 ultras installed- 768mb (in think) each.