EDIT: Ok, so apparently what I need to do is create a layer mask on the alpha channel, do whatever it is I need to do to the Alpha channel to get it to at least resemble my jerseyALPHA.bmp file, and then apply the layer mask. That's all fine and great, except that I have no idea what to do the make the layer mask like the jerseyALPHA.bmp
EDIT 2: If someone is willing to merely edit the .dds file for me so that the alpha channel is done properly, I would be more than happy to send all the requisite files.
NOTE: This is also my first time using the GIMP for anything other than image file conversions.
EDIT 3: I decided to proceed without actually solving the alpha channel problem, just to see what would happen. Well, aside from FshX not wanting to import my .dds file (which I replaced instead with a my jersey's finished .bmp file), everything seemed to be working fine.
Observe:



But upon closer inspection...
Oh no!

I knew about the shitty cropping, and planned on fixing it afterward, as well as the logo interfering withe number. But the size!? WTF? As far as I know I used all the right settings (i.e. 256x256). I repeat, WTF?