Gmod doesn't seem to like this

Fairly simple story here, I’ve watched a friend play Gmod for a while, and decided to get it myself. It worked fine for me, until my friend wanted to play online and sent me the files they were using:
http://www.mediafire.com/?46z6od7ft2nayse (fairly large)

I merge this into my gmod folder, and now the game crashes right after it says “Preparing to Run Gmod”

Heres what doesn’t work:
-Disabling Firewall/Security
-Reinstalling it (both partially, and completely)

Advice?

Question: Why would you use the files that someone gave you called “garrysmod.rar” Is he TRYING to downgrade your gmod?

What? Their just files aren’t they? o.o

I think, a real life friend of him, sent him a folder with models and shit?
I don’t know, because I didn’t download the file, but still.

Thats pretty much it, cept now Gmod keeps crashing.