Converting VMTs to JPEG/BMP/GIF/whatever?

VMTs are just text files that link to VTF files - open the VTF (should have the same name) in Photoshop (need a plugin) or VTF Edit, then save as in PS or Export (as tga) in VTF Edit.

You are looking for VTFedit

basically what honey said, download this. when you open the vtf in this, you can export it as a format of your choice.

If you're wondering how to open the vtf in the first place, you'll need this. open the team fortress 2 materials GCF, and then you should be able to extract the VTF from there.