the others have already answered your main question, that 10.4.11 is the latest OS that will run on your Powerbook G3
- but I just wanted to comment that I got many years of good use out of my Pismo, even though it needed a few repairs along the way it is still working (now almost 10yrs old!). In fact, I used it temporarily as my main home computer last month while my iMac was in for warranty repairs.
my point is that if your Pismo hardware is still in working shape, install OS X 10.4.11 on it and you can keep using it for many things. it's a bit slow by today's standards but otherwise I think it's a great machine.