If you are looking for a specific model, you might have luck asking the author to convert it to 3ds/OBJ format for you.
If you want to do it yourself you'll needs 3ds Max 4 or 5, Milkshape, or GMax: All of which can support MOD files with the proper plugin.
Make sure you check the permissoins thread, as some people do not allow conversions of their model, whereas some folk may want you to check with them first.