Wow - interesting. To get to SQL Express you need to come from no earlier than 7.0 - upgrade from 7.0 to 9.0 (SQL Server 2005) is the most backward-looking upgrade path that's supported. I discussed how to get to 7.0 with my wife Kimberly Tripp, as it's before my time, and she advises installing 7.0 and then using the migration wizard from 6.0 to 7.0 - if that's supported. One issue you have is that nothing that old is supported at all, so if you run into any issues you'll have a hard time finding support. I know some people in Product Support who were around then - let me know if you hit any problems and I may be able to to get you some limited help.
