Ok let me help...
Custom textures require 2 files:
Texturename.vtf
Texturename.vmt
Originally the VMT starts out as an empty .txt with the same name. You simply open Steam, drag the .tga file from this folder:
C:Program FilesValveSteamSteamAppshabboisourcesdk_contenthl2materialsrc
onto VTEX and it will out put the empty .txt there and the .vtf here:
C:Program FilesValveSteamSteamAppshabboihalf-life 2hl2materials
Collect them both and edit the .txt so it has this:
"LightmappedGeneric"
{ "$basetexture" "yourfoldername/yourtexname" }
Foldername could be anything e.g. mytexes, DarthRevan etc..Whatever you name it it must be in THAT same folder in both materials folder.
Then rename it to .vmt and copy these two files (vtf and vmt) into both folders. Thats IT
Here are two videos I recorded a bit ago:
http://rapidshare.de/files/16003685/Customtexture.zip.html
Unfortunately I had to film two video's since when I recorded that Valve had updated Steam so it meesed up my VTEX...
But you'll understand...
Now the BSP requires both files and you can either include them in your map using BSP burner or something..Ask Rabid or Cap'n or just follow my tutorial. It may not be the solution to your question but you might get a better understanding of how textures work.
You need a VTF viewing program to view the image..I believe there is a Photoshop plugin...