Here is the basic precedure for locking a differential...

Supplies:
CA glue (super glue)
Your Diff...Duh???



The basic idea here is to glue it at the spider gears. I went into photoshop and edited it a bit to help. The red circles are where you want to put a drop or two of glue and the black lines are the ends of the spider gears.

Good luck.

BTW: this mod helps dramatically with acceleration and torque and is awesome for drifting, but if you lock the front it will kill your steering