Aha! Got it. Your X3100 is doing it dynamically - it takes memory as it needs it. You can set the maximum it can use in the graphics driver, which seems to be set to 32meg.

You can raise it to 256meg if you want, don't go any higher though. The driver goes higher than the hardware can handle so you're just wasting RAM over that.

While your in the driver check the quality settings, make sure they're not set to any form of performance mode.