Can you adjust dedicated memory on XP

Is it true that you can change how much memory is dedicated to video and other functions. I see that there is a sliding scale that give you an option on how many mb's/gigs you can dedicate to system restore and I thought there was a similar way to change how much memory is being dedicated. Here's the thing I have the RAM maxed out at 4 gig's BUT it's only seeing 2.91 gigs. Yes I know that a 32 bit OS never truely see's 4 gigs because of limitations in the OS but to be using 1 full gig on video when I have a deicated video card seems like a waste. If I could dedicate more RAM to the system and less to the video it would be making better use of the memory.