Completely identical, with two limitations:
1) Limited tech support straight from MS. Don't remember terms, but I don't know anyone that's ever needed TS at all, let alone more than twice.
2) Ineligible for upgrade version once 2007 comes out.
It does not expire, and it works with all of the standard Office add-ons. Oh, and the 2003 boxes that ship now can actually be installed on three computers, instead of just one.
I don't think you get Access with student and teacher, and there's limited xml functionality compared to the full Office Professional.
The 3-machine license is very nice though, but if I were you I'd download the 60 day trial version and then pick up the family version (replacing student & teacher) of Office 2k7 when it expires.