Sorry, I was using the add button to add the main firmware to SETool like I said, but it took me a while to realise I adding the vkp file using the "Firmware Upgrade Pack" box, instead of the "MISC" box.
Now that I did it correctly it worked great! Unlocked!
Thanks Simox for this great guide on doing this. Now I just need to figure out how to get rid of the annoying T-Mobile opening jingle (I'm sure I'l figure it out).
Thanks again, Gollach.