I'd take a look at the existing Gossamer Forum import scripts (admin/GForum/Import/*.pm). Depending on your level of experience with Perl, the easiest might be to try to adjust one of these to work. Alternatively, if one of the supported forum scripts has the ability to import from Discus, you could do a double-import through that other forum.
Jason Rhinelander
Gossamer Threads
jason@gossamer-threads.com
Jason Rhinelander
Gossamer Threads
jason@gossamer-threads.com