In this case, it's not "data" that concerns me. I don't keep anything important at all on the Windows box. I am concerned about the software installation -- WinXP and all of the drivers and apps that took forever to get into the machine.
I can back all of that up easily, by booting Linux from USB and using rsync or mirrordir to replicate the filesystem onto another (ntfs) drive.
What I don't know how to do, is how to re-install the WinXP bootloader on that drive. I suspect this can be done by booting from a WinXP installation disc (CD), and then issuing some magic incantation to rewrite the boot sector etc..
Making a backup is trivial just using standard (free) Linux command-line tools. Maintaining the backup is similarly easy. But getting WinXP to boot from the backup image is my only dark area.
I suppose I could just bit-clone the drive once, to an identical drive, and from then on use rsync/mirrordir to refresh the backup periodically. That might work, but I really know almost nothing about booting requirements for MS-Win.
Thanks guys.