your AGP aperature ( from how i understand it ) lets you tell the system how much system ram your drivers will use to run graphics accelleration.
my settings were originally set at 128mb, the next option up was 256mb, since i have 512mb total i figured it wouldn't hurt to try.

you access the advanced features by entering BIOS settings on startup. when you have the CMOS screen up type CTRL+F1, then screen will flash off then back on, with a few more options.
the post i read said the features were on Gigabyte motherboards, i don't know if it's the same for all brands.
has anyone else heard anything about this?