I think it's key that your backup system be external to your computer, for two reasons. One, if you have a catastrophic event within the box, you could conceivably damage the backup disk (e.g., power supply surges) and Two, if your computer crashes, you can take your external disk to Kinko's or somewhere, rent a backup, and keep working.
to the O.P. question: iMac G5, 2GB RAM.


Dual Core is good,
