Aloha, I am new to this forum (t-minus 23 hours) and I too am currently playing with an Imac G3...Mine is a 400MHz though. I am currently running os X 10.4, with no noticeable issues yet. Apples site stated the minimum requirement for OS X 10.4 to be 256MB Ram, Firewire port, and 3+gigs of HD...