If you have 2 seperate pics you can set this up in MED pretty easily. Open the model in med, go to 'Manage Skins'. You'll need to have to skins setup. If you have have skin0 there, just hit new skin to add skin1. Otherwise do it for both. Make sure you click the 'texture' box for both. In skin editor add one pic into each slot with file>import. Right now everything is assigned to the first skin. Select all the polys you want to be on the second pic, click 'skin1' in 'Manage skins' then click the 'set skin' button. Now those polys are assigned to the second skin.