I try to made a skin but i got a problem...

Hello everyone, recently i get gimp to trying to made some hexed skin, I watch some videos to explain me how to made the skin and the hexed
but everytime i try to open a materials file with gimp (and photoshop now), i receive a message like: Its not the right kind of file.

I got some program like:
GCFScape
XVI32
VTFEdit

I don’t know if i need a another program for that or is it just me that doing wrong.
I will appreciate if someone help me.

P.S.: Sorry if i had a bad english : /

VTFEdit should work.

[editline]5th November 2011[/editline]

Open VTFEdit, Click file, then export, Export it to where you want as a TGA. Then open in gimp. Use import to save it as a VTF again