u wanna set it to 64mb on your/most systems.
What it is is when your vid card runs out of ram it uses textures/or whatever stored in your comp ram 1st (slow) or if u set the agp ap higher than the ammount of ram u have it stores more in your hard drive cache (even slower)..
well thats the idea i got of how it works........
(prob not far off the truth though)
JAZ