|Windows already uses system memory for "virtual VRAM." Just as Windows uses the page file on your hard disk as fake RAM when you run out of the real stuff, the shared graphics memory is used as fake VRAM when you run out of dedicated memory on your graphics card.|
You can take a look at how much RAM Windows shares with the graphics card under Video Adapter Properties. Haven't checked in a while, but I believe it's around 1.5GB on my main system.
If you're after better performance, you'll need a new card.
Super PIII | Unlocked ES Tualatin @ 1.8GHz (150x12, 1.65v, 512K L2)
2GB PC2700 | 500GB | Radeon x1950Pro | Apollo Pro 266T | Win 7 Pro