In that case, you'd want to unpack the pak0.fpk file, and then convert the .dds picture to something like jpg. I'm not on my computer right now, so I forget the names of the free programs I downloaded to do that. If I were at home I could just upload a jpeg of Sphener here.
Now that I think of it, you may have to trim off some gray space at the bottom after converting it. I don't recall having to do that when I made Sphener my desktop last fall, but I didn't when I make the Thanks screen my desktop lat week.