I don't want to disable Apple software update, I just want to prevent myself from accidentally overwriting my iTunes 10 with a working Party Shuffle/iTunes DJ with the new iTunes 11. I have iTunes 11 at work, where it doesn't really matter what I've got installed because I can't play music during the day, and I've tried to come up with some combination of smart playlists that effectively duplicates iTunes DJ... but it doesn't work. The tools aren't there.
So, how do I do it, how do I selectively block updates for iTunes 11?
Edit/Update: All the helpful answers here are no longer useful.
Don't do it. Later versions of OSX ship with a newer iTunes and rolling back to iTunes 10 breaks some aspects of Software Update. I ended up having to reinstall and use Migration Assistant to restore from Time Machine to get a fully working system again.