I am typing this on my iBook G3 500mhz. OS 9 and X came on it when I bought it. I would caution you though if you are thinking fo getting one. OS X is tolarable when you have a system this old. My laptop is 4 years old. Why it is fine to surf the net with, using office, iMovie, etc. is almost out of the question. They will run, but slowly. Not to mention the fact it only has 8 meg. vram. Kills of whole quartz fun.
When I picked up my iBook, I got it with a 10 gig. hardrive, 128 meg ram, and picked up a few softwear titles. It cost me in all 2800. Now you can get one 4 times as powerful for under a grand. Man how times change. But I still love her.
My first mac, I will never go back.