Here is some information regarding the Xbox360 JTAG exploit
Simple Db-25/cat5 Lpt Nand Dump/flash Cable Tut
JTAG HACK
JTAG/freeBOOT/XBReboot FAQ
And a way of getting the DVD drive key from a JTAGged box
DVD Drive Key Recovery
Here is a post with information regarding a fuse to remove
Shall I Remove R6t3 After Successfully Flashing Xbreboot