My recommendation is to buy a USB 2.0 or Firewire external hard drive of equivalent (or larger) size as your PowerBook's. They're so cheap these days. An 80GB hard drive won't set you back more than $50. Double that amount and you could even get a pocket-sized external hard drive that you could bring along in your travels.

Then, once a week or so just copy your home folder over to the external hard drive. No need for any kind of backup software.