I think the question is about backing up the Mac, not the XP machine!
Apple's Disk Utility can create a disk image of your drive. Carbon Copy Cloner and SuperDuper can do the same thing. Then you can boot off another boot volume (such as an external hard disk, or a Panther install disc) and restore from that disk image if you need to. That's basically the process used by system administrators to clone systems, but it works great for backups, too.
Note that .mac backups don't create bootable backups, nor does Retrospect, the only "real" backup program on the Mac. (By which I mean one that does incremental backups, backup to tape, etc., as opposed to apps that just clone. There are many of the latter.)
tooki