Leave it at 64M
The only thing that I know of that benifits from having it set higher is 3DMark2K (64M texture test).
Games will use the 32M of vid card memory, which is a hell of a lot faster than system memory, and will only access the system memory if neccassary. (spelling??)
But in most games etc.. you would have to be running with the graphics settings cranked up high for this to happen.
But hey, at least there are a 'few' ways round this.
Q3: Use texture compression.
UT: Use openGL renderer with s3tc.
This may change however as more and more games are coming out with flashier graphics. And vid cards are being made with 64M and even 128M of memory.
P3 800e @ 1 Gig with Alpha PEP66 (YS-Tech fan: bloody noisy)
256M PC133 Crucial
TurtleBeach Santa Cruz
Iiyama VisionMaster Pro450
Corsair PC2700 cas2