Well, first thing first, go get yourself an AMD setup. Sell your G4, to your grandfather or perhaps a mean uncle, and get like two AMD XP 2000+ rigs. It will be very cheap, and cut your render time to 1/10th of what it's at now. To cut your render times down, try making a different kind of tree perhaps? Check to see if Tree Lab trees render faster, although I doubt that would be true. 624,000 polygons isn't really a big scene, necessarily, although polygon count has less to do with render time than your light setup... Just some ideas! (don't get offended about my fruit-based PC comments, you'll live my friend!)