Ok, this is the last thing I'll say on the subject (probably).
Forget everything I've ever said about hosting Time Machine backups on a shared drive. Yes, it's technically possible. But, trust me. Don't do it. Just don't. It's not worth the heartache.
Go out and buy a Time Capsule. Wireless backups that actually work! I've been running mine for two months now, and I haven't had a single hiccup. Much, much better than the shared drive option.