If you're a .mac member then you could try Backup. If not give Carbon Copy Cloner a go. It copies the whole drive as opposed to just your user directory however, but it's received favorable reviews and it also serves as a useful way to boot your machine into a working state should anything go wrong with the PowerBook.
Note however Backup won't encrypt the files. To get around this you could backup to an encrypted disk image.
Apart from Backup and Carbon Copy Cloner that Matt has mentioned, I would also suggest taking a look at
SuperDuper! (my personal preference) and/or
Deja Vu.
15 1.25G/12 1G PBs, Mac minis, iBooks G3/G4, Mac OS X (10.4.3) Cube, TAMs, iPods 2G/4G, iPs, AEBS, AX
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Backing up
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