You need
SimPE and the mesh exporter; home site of
SimPE is:
http://sims.ambertation.de/
You can probably get both in downloads here too; but mesh exporter plugin for
SimPE might be in Beta Testers forum.
There are mesh exporter and importer plugins for
milkshape, by wes_h, look in Beta testers forum, or use search -upper right of page.