I have OSX 10.2.5 on two of the original iBooks. I recently upgraded RAM to the new 512 chips available for the early iBooks (avail at OWC, as well as other online stores). Everything works wonderfully. Of course 300MB is now a tad slow, but not slow enough to worry about, and I definitely recommend the RAM upgrade to go with it. If you have not already installed a larger hard drive than the original 3GB or 6GB, now is the time to do so.