I honestly don't see the problem. You can get Windows boxes dirt cheap and unlike what the zealots will tell you, Windows XP *is* stable enough to act as a file server. Heck, I ran a file/audio/home-automation/caller-ID-announcement server in my parents' house for years under Windows 98, and even that only needed rebooting once every few months. They had occasional neighborhood blackouts more often than that, so the problem was even self-correcting!
Unless there are specific things you really want, like the aforementioned desire to share HFS+ volumes and use Time Machine, then any machine capable of serving files would work fine. If you "feel dirty using Windows" or knowing that your files came off a non-Mac machine, then you need to get your head examined, because in the end a computer's just a computer!
