XRaid is a supported configuration for Time Machine, isn't it? You don't have to enable this hack, just be running Leopard on the server.

I believe leopard server is a possibility, but over the network? Anyway, I'm running Tiger Server on the Xserve, and have no plans to run Leopard any time soon. Also, I'd love to set something up for my home computers to back each other up via the network. Still not perfect (i.e. off-site), but better than the half-a$$ed way I'm doing it now. Currently I'm just burning CDs of stuff I think is important. I could set something up with rsync, etc., but I've been so looking forward to Time Machine being my backup of choice, both for ease of use and as an example to my PC using friends!

You don't need Leopard Server to use Time Machine over a network. Just regular Leopard is fine. I do this at home. It's a supported configuration (in the help files and everything).