What do you want to do, and what are you going to be running on it?
Mac has the iBook G4-which range from about $950-$1,200 (US) ish, and the and the Powerbook G4 which ranges from about $1,400-$2,300. The Powerbooks are a little more upgradable than the iBooks.
You'd most likely want to upgrade your memory by a gig or so, things will run much smoother the more you have.
I'm more familiar with the PC desktops than I am with laptops (i'm kind of a Mac guy), so maybe some other people have some suggestions if you want to go the Windows route.
Think of what programs you want to run, and start from there since a lot of the DAWs are platform specific (like Logic Pro 7 is Mac only). Other than that, decide on how much memory you will need, and update a bit from what you think so you can keep up with software updates. Feel free to PM me with any questions.