I love my Mac, and I like TimeMachine as the best new feature (I use) from Leopard.
I also searched for such a solution for Windows (e.g. for my parents or my sisters laptop).
My search has an end, I found rsyncbackup.vbs from heise.de.
I know, it's not a solution, jus a script. but I'm sure, I can adapt it a little bit, so it would be useable for my family (e.g.: in startup-script, check if target-disk is available, etc.)
We will see...