Using Windows on a PPC Mac is not a worthwhile project anymore.
You end up with Windows hardware created completely in software. It's not something that you would ever enjoy, as you end up with an emulated PC operating at something like 200 MHz, if you're lucky! XP would be a hopeless dog.... (no offense intended to any dog, but it would be dog-slow)
You should use this as a good excuse to upgrade to an Intel mini, when you would have about 6 different options for using Windows, most leaving you with a good-performing PC, if you really need it!