I own a 20" iMac G4 with a 1.25GHz processor, 2GB RAM, 320GB hard drive, and running OS X 10.5.8 Leopard. It's pretty fast for being 8 years old but the only real problem I am having is playing videos with large dimensions. I tried playing a smaller video and it worked fine. I have repaired permissions, searched for different ways to optimize the os, deleted unnecessary items from the hard drive, tried different video formats, and different players such as VLC, Quicktime, and iTunes. The problem still persists. I have even tried youtube videos which seem to be able to play with less lag once I allow them to load. Is it simply because I'm trying to play them on an older computer? If so, it doesn't make sense to me why youtube videos would be able to play better (do those only depend on internet connection?). I feel like I've tried all I can and I didn't know where else to ask.