If your xbox is a version 1.6 (excalibur video encode located at the back of the board) then you have no option but to do a rebuild.
You have 2 options here, you can either use an lpc rebuild board, these come with the smartxx chips and xecuter chips. You can also buy them seperatley. If however you are impatient like me and just want to install your chip then you can do a wired rebuild.
First of all lets go through the rebuild board, take a look at the picture below. it is soldered to the bottom of the motherboard as in the picture (arrows show where to solder), the D0 wire from the chip is then soldered to the d0 pad on the rebuild board ( one end on board, the other on the chip). Wire the other points of the chip as you normally would according to your chips install diagrams and your away.
For the wired install it's pretty similar, just solder wires (I reccomend 30awg wire) as shown on the picture below. Where there is a yellow line, that is meant to be a wire, the LFRAME (d0) should be soldered to the point on the board as shown, and the other end to the D0 point on the chip, then install your chip as usual.
If your motherboard has Hynix memory chips (2 on top, 2 on bottom) then you have a 1.6B, the soldering is all the same.
Source: xbox-hq.com