I tried Ubuntu a couple of times on my iBook and iMac over the years. It's been a while but I think I had video problems with both (the iMac for sure). Kubuntu especially was very buggy. I fared better with plain Ubuntu but not enough to run them much longer after installation. They might have ironed these problems out by now so it's no harm to try it. If it doesn't work out you can go to OS9.