I'm graduating from high school this year as well, and I bought a Rev. A 12" iBook G4, but will be selling it this summer in time for college so that I can get a PowerBook. Before I aquired my iBook, I had a Rev A. 12" PowerBook G4, and I can say that hands down the PowerBook is the better machine.
You will spend a bit more, but you really can tell the difference when it's in your hands. The PowerBook is smaller and lighter and more powerful, and it leaves open the option to really get some great performance out of your machine if you ever decide you want to do more demanding work.
All this year, I've been taking a video production class, and convinced my close friend to switch to mac about the same time i got my iBook G4, and she got her 12" PowerBook G4, and we both were just as hard on our computers, throwing them into and out of our bookbags just wrapped in a towel or pillowcase at times, running around with them in the hallways, needing to do on-site editing, and of course using them at home, and her PowerBook has actually held up just as good as my iBook build wise, and definitely beats my iBook cosmetically. My iBook is full of scratches and shows dirt easily, her PowerBook looks brand new. (and no, it's not because I am just a dirty boy lol) The keyboard (space bar, enter key, the keys that get hit the most) along with my trackpad show very obvious wear and tear, as they have been worn down to a shiny smooth finish as opposed to the usual flat white.
I'll be selling my iBook G4 to get another PowerBook G4 for college (12" probably, but if i can, go for the 15") and I would advise u avoid the iBook and get the PowerBook as well. Of course, "performance wise" for just Word or spreadsheets the iBook G4 is fine, but the PowerBook is lighter, smaller, faster (especially when doing more processor intensive tasks if you ever need to use them), and built better, Hope this helps!
LMV (Class of 2004)