How would i get props into Source?

Hey, i have some Weapons from some game (Can’t remember…) and wan’t them in Gmod / SFM / Source, But i forgotten it ALL.

Explain-ing Better :Well, i have some props from ACIII But i wan’t them in gmod / SFM Not 3DS MAX, How do i get it into Source?

But to be perfectly honest you could have worded that a LOT better… Lets start with the basics, what format are the models in currently?

(User was banned for this post ("image macro" - postal))


[editline]2nd June 2013[/editline]

Well… i did you’re tutorial, but i got this error on guistudiomdl