Tutorial written by : Exobex (posted on forums.xbox-scene.com)

If you've got an inexpensive "homebrew" mod such as the LPCMOD V2.0, you may find that the BIOS is write-enabled, with no solder-points to allow you to protect it.

If this is the case, and you're worried about M$ meddling with your hardware ("Oops, was that your BIOS I just flashed? Sorry!"), you may want to try this:-

Open your Xbox
Remove the 49LF020 chip from your mod's IC socket, MAKING NOTE OF WHICH WAY ROUND IT GOES! It should only fit one way, but you never know...
Cut a 3mm x 20mm strip of PVC insulation tape
Fit this strip over pins 7 and 8 as shown in the following image

click image for full view

(if the tape is too wide, you can cover pins 9-12 as well, they're not needed)
Refit the chip the right way round
Reassemble your Xbox

The pins you've covered are the write-protect pins, if they are connected to 3.3V (as they are in the LPCMOD V2.0) the chip can be reflashed. If connected to 0V the chip is write-protected. If disconnected (as in this case) the chip should is also write protected.

This has been tested using Evolution-X. Without the tape, the chip can be reflashed. With the tape fitted, the flash process hangs when it tries to erase the chip.