The differences in the GT and The LX are all in the body styling. The GT has the ground effects, which add 100 pounds, with the fog lights as an option. In addition, the GT has the option of having the lower portion of the car painted grey. The LX on the other hand, does not have the ground effects like the GT, saving 100 pounds. In addition, the lx does not have fog lights on it. Also, the LX has what looks to be "Rubber" striping around the center of the car. If you are interested in learning about more of the differences from the GT to the LX, you can visit the Mustang GT registry at:
http://www.mustanggt.org/main.htm
Under the " need to find something fast? " Select the pull down menu and pick " Differences between GT and LX Summary". Hope this helps you out, sorry if I talked your ear off. Also, if I am wrong, anyone, please correct me.
-Jason