Bumping that RAM up over 256MB makes OS X bearable, but it will creak along with as little as 192MB. Once you get over 300MB, you'll really start to notice a difference in responsiveness. Adding a faster hard drive, CPU and video card helps a lot too, but RAM is IMHO the best first upgrade, primarily because it's the best bang for the buck spent. Throw three 128MB sticks in it; they're essentially free these days. NB, 256MB is the largest stick that will work, and they have to be single-banked (usually single sided IIRC).