Overgrown LDF file won't shrink

I am looking for an SQL 2005 expert.

I've got a database that is just under 1GB in size but the log file
(.ldf) has consumed all the remaining (400GB) disk space.

We have made sure the DB is set to SIMPLE, finally attached an external
500GB disk drive to do a backup and still can't shrink the log by more
then 12GB. The DB checks as good. As soon as you do anything (like an
export) the log file jumps back up to eat any free space.

This is for an application that has been replaced but must be kept for 5
years for required reporting functions. The actual data shouldn't be
getting changed so not sure why there would be any log growth.

Anybody got a way to preserve the DB contents and shrink the log back
down to a reasonable size?

BTW the current app won't run until we get the free space back.

Thanks.

Roger Vicker, CCP