If you install iTunes 4, it adds several new schemes to your list in Internet Config.
[pudge@bourque pudge]$ perl -MMac::InternetConfig -le 'print join "|", GetICHelper($_) for qw(itms itmss daap)'
(hook is the creator ID of iTunes.)
itms stands for "iTunes Music Store" and allows for links like the ones you see below. Click on the song title and iTunes opens to that song in the store; click on the artist or album and get that. Of course, small spelling differences can mess things up, and many songs/albums/artists are not in the store, but that's life in the big city.
I imagine that itmss is for secure transactions. daap is used for playlist sharing. Both itms and daap are being reverse-engineered; itmss is more difficult since you can't just peek at the TCP/IP traffic, seeing as how it is, you know, encrypted.