You added a shitload of RAM; good. To answer your question, adding some RAM to compensate the lack of video memory is a silly idea if you don't do what follows:
- be sure you have an AGP card!
- if it's an AGP 2X card, be sure it supports Sideband (might require flashing the video card BIOS)
- enable all working AGP features on your motherboard (long experiments here if you dunno the specs of your card)
- switch 'AGP aperture size' to 128 or even 256.
That's easy. Now, harder: increase your memory transfer rate, by using 133 mHz instead of 100 mHz and try lowering the CAS as much as possible (goes for both SDR-SDRAM and DDR-SDRAM).
If your system holds and the graphics don't hang, it's cool.
Even harder: overclock your video card (memory and chips), starting with memory. Proceed with caution (if it hangs, lower the settings and find a larger fan)