Alrighty.

I've made a few materials in photoshop, they all have alpha channels. Example: The graphic is white with blue variations (snow texture) and in the alpha channel is channels, I have a black background with white spots (So basically it should come out as random spots of snow).

Thing is, I have no idea how to configure my .vmt

Here's what I have so far:
"LightmappedGeneric"
{
"$baseTexture" "maps\dod_stammlager\stamm_snow1"
"$vertexalpha" "1"
"$vertexcolor" "1"
"$surfaceprop" "snow"
}

I'm not sure if "$vertexalpha" "1" is right.
In-game, the transparency works and all, but the texture is black (as is the texture itself was ignored and the alpha was applied to a pure black surface) I think I'm missing something here...

(PS: I'm not a Photoshop newbie, I've been photoshopping since 4.1 ;) )

edit: Also, the texture and transparency show up fine in Hammer..

Ah, I feel stupid, it was the $vertexcolor that I had to remove :o

use VTFEdit

i was going to say the same as Unk, using VTFEdit is handy for automatically making the .vmt just by clicking on checkboxes for what properties you'd like in the texture.

Also, i found for a transparent texture on mine, that i'm using "$translucent" 1 instead of "$alphatest" 1. I'm not sure of the difference, they both did look a bit different (i think the alphtest made sharper edges around the transparent bits) but they both produced transparency.