OR you can just use Noesis.
Example take b_batt0.bsp out of the pak file. Open it with Noesis then File --> Export --> MD3 and leave all options default except what directory you want the export to go. DONE! You can open said exported b_batt0.md3 right back into Noesis to check it out. Word of warning don't try to export to any other format because it will make more work for you since Noesis screws up the UV mapping on export. To fix it you would need to import into blender to fix that so just stick to md3.