Never tried a downward migration.
To mount a db, the sql server must have been installed with the same language and sort orders that the db was originally created with.
So, the options are:
1) try mounting the db. it will soon be apparent if this approach will work. if the db comes from a commercial app, ask the vendor if it is possible to use SQL2K.
2) mount the db locally on SQL Express, export the tables using bcp to text files, then import the tables on the server using bcp. you will need to create the tables first.
3) mount the db locally on SQL Express, use data transformation services or replication to move the data over on a one shot basis.
The options are listed in my order of preference if it were me