Congrats on the great find! I used to have one almost identical to that. I upgraded it with a 500GB hard drive and 2GB of RAM and it did really well for me.
I acquired 2 17" G4 iLamps for free and in my haste to upgrade I sold of both. I really regret doing that. While the 20" is the paragon to find for the G4 aficionado, the 17"s are still amazing machines. Stick with 10.4.11 and pimp the ram, cram a 7200 drive in there and love the goodness of one of the best macs ever made.
Good find at an amazing price!
Great find, man! I always wanted one of the G4 iMacs...my friends parents had one and it was the coolest thing back in the day! Definitely upgrade the RAM to 2gigs and replace the PRAM battery. If possible, also replace the HDD with a 7200 RPM or a SSD!