Custom Material tool?

I was wondering how one would add a custom texture to the material tool in Gmod.

Thanks in advance.

Edit:

39 views and no replies?

Sorry for the big bumb but I was wondering the same thing and could not find instructions on how to. Any help?
This could be extremely useful to me if I knew how to do it.

Find the wanted texture, convert it to the appropriate file type, and place it in the folder where the other ones are located.

So how would I make these work? http://www.garrysmod.org/downloads/?a=view&id=84430
Be a little more specific please.

I still need some specifics.

Come on, nobody will help? …sigh…

Most of the time, you can just download an addon with the desired material, and it should automatically appear in your materials foler. Example - The downloadable entity Antlion Thumper

What? There’s a way to make the materials or texture icons show up in the material STool, all I need is a tutorial or something so I can add any material I find and add it to the STool.