I made a quick tutorial for making short shorts for Live 2003 (the technique still applies for Live 2004). You may find it helpful...you can find it here.
Jowe made a jersey creation tutorial for Live 2003...you can find it here.
I'm not aware of any Live 2004 tutorials for making jerseys...
Have you gotten this to work for 2004? I'm trying to make mid length shorts for some 80's players and I keep getting some trimmings at the bottom of the transparent area....what could I be doing wrong here?