I've started working on Blender, just creating models. I've been looking for a MDL Importer/Exporter, none of them seems to work for me. I think I use 2.5, and I only use a Mac. What I'm trying to do: -Make a Team Fortress 2 Mod.
http://www.moddb.com/games/half-life-2/tutorials/how-to-import-source-models-in-blender As for exporting, I've never done that, so check the Valve Developer Community page. http://developer.valvesoftware.com/wiki/Blender_SMD_Tools and the SMDTools page http://code.google.com/p/blender-smd/
this is all you need than. http://code.google.com/p/blender-smd/downloads/list than you will need to learn how to write proper QC files so source sdk can compile your exported smds. and than make your materials and textures of course.