dongmin said:
The Powerbooks have the advantage of being able to use an external monitor for extra desktop space
you can hook up iBooks to external monitors you just need to get the cable, which albeit is costly, however PowerBooks aren't the only Mac'tops that can use an external display. I personally think that you should spring for an iBook, they are tougher and will serve you well, I love my PB but I beat it to all hell JUST carrying it around with me. Check out the old G3 900's (if you want to save some cash), or the ibook g4's. While OS X is a RAM Gusher, with about 512 you should be ok. I say Spring for the iBook g4, or the older model G3, and put the money you save into buying a 2nd gen Powerbook g5 when every they decide to show up.
EDIT: one thing of note, external storage may become a necessity when you get these ibooks/ small PB's try thinking about how much storage you will need.