Although it appears that this community doesn't really have much of a HL2 fan base I still think this might be helpful to someone who goes by here. Anyways here's how to do it.
Hooch's L4D2 Decompiler.
If you are using 3ds max 2010 or lower you need to get a SMD importer for this to work or you can use milkshape to export into a obj or 3ds file.
Now first you need to do is go browse for the model. Once you have done that then you need to go select a output directory. Do not put it in the same spot where another .smd file is with the same name you risk crashing your compiler.
Then you go into milkshape and hit import. Then go look for your .smd file that is a refrence usually named ref or its the biggest one. Then hit export in milkshape to export into another format.
If you are decompiling for l4d2 or l4d or CSGO you will not have a.dx80 file! This is needed to decompile the models. A good work around is to copy the dx90 file and paste it. Then rename the 90 to 80.
Then you are all done!
Caution the decompiler has some issues with certain models to where it refuses to decompile. Sometimes it doesn't load the qc file which isn't needed if you don't plan on recompiling for the game you got it from.