Oh wait i re-read the post you need a transfer cable / usb and EZGT or Hadzz GT editor to mod your gamertag I suggest you use Hadzz GT editor look in the xbox free programs section. As I never have had a Jtag I cant really comment
acualy i give jtagging an xbox like 4/10 it is easier then modding controllers what i did before. u just gotta know the good ways to solder and it is really simple