In the world of total illogic which is that of our client, the requirement that required the data from this massive 2.9 gig BAK file is no longer required. However, I had nearly solved the problem based on all your suggestions. I downloaded a copy of MSSQL 2K Trial and was in the process of dumping the database into a more negotiable format. I originally tried MSDE, but you're limited to databases smaller than 2 gig.
Getting back to Perl, though: Looking through the BAK file in a hex editor, I found it difficult to see many patterns. I concure that it would be very non-trivial to write a Perl parser for such files. However, it ought to be do-able. If anyone had the time and interest, I'm sure folks who like MySQL or PostgreSQL would be fans of a utility that would let them easily migrate an MSSQL database into something a little more open source.
code('Perl') || die;