Another oldschool method is use an original vtex.exe (valve texture compiler) directly from Beta.
Go to /anon-hl2/hl2/, create new folder and name it "materialsrc" and place your texture source file here (i recommend to use .tga for texture sources). Compiled .vtf files from tetxure sources that placed here will appears in /anon-hl2/hl2/materials/ folder.
You can create subfolder, if you want (e.g. /anon-hl2/hl2/materialsrc/myfolder/), but dont forget to create similar folder in materials (e.g. /anon-hl2/hl2/materials/myfolder/)
Go to /anon-hl2/bin/ - find vtex.exe and click Copy. Get back to folder where you placed texture source file (e.g. /anon-hl2/hl2/materialsrc/myfolder/), right click - Paste Shortcut. That's right - you just need shortcut to vtex.exe here, not the actual copy of vtex.
And then just drag your texture to this shortcut, and you will see command line. You can find properly compiled .vtf file in /materials/myfolder/. And then just create .vmt manually.