Getting Inside
When you look at the bottom of your Xbox you will realize that
there are no screws visible, that's because MS has hidden them.

You will find the 6 hidden screws in the following positions:

1 under each rubber pad - you will have to peel these rubber
pads off to get at them - and 2 under the stickers.
So unscrew these using a Torx 20 screw driver and lift the top
off your Xbox.

Hard Disk Removal:
You will now get the first glimpse of its guts! The big box
on the left is the DVD drive and be big box on the right is
the Hard Drive.
First thing to do is to unplug the two cables from the back
of the hard drive.

If you find the power cable (that's the one with the red,
yellow and black wires) hard to remove or do not want to
risk damaging it then remove the Hard Drive from its plastic
stand.

To do this undo the screw shown on the diagram below with a
Torx 10 screwdriver to free the Hard Drive's stand.

The stand should now be free from the rest of the case.

Then remove the 4 screws either side of the stand to remove
the HD.

Now you can remove the power cable safely.

After that put the HD and its stand to one side. At this
stage your Xbox should look like this:

DVD Drive Removal:
Start by removing the big cable from the back of the Unit.

How undo the screws (Torx 10) at either side of the front of
the unit to free the units plastic tray.

Move the unit out the way and detach the yellow cable, I
found it easier to unplug the yellow cable from where it was
plugged into the main board rather than where it plugged
into the back of the DVD unit.
You should now have full access to your Xbox's motherboard.

Getting to the back of the main board
The first thing we need to do is remove the 11 screws from
the main board using a Torx 10 screwdriver. Here are their
positions:

Next we need to unplug everything from the main board.
So start by removing the two white plugs which are connected
to the small vertical section of the main board. This small
board can now be removed fully.

Now we need to unplug the big power cable. Because this is
wedged in I found the easiest way to unplug it was to push a
flat head screwdriver down the gap to release the plug.
Don't worry if you hear things snap, the plug will hold its
self in even without the clip.

Unplug all the other things connecting to the main board
(not forgetting the plug from the large black fan at the
back) and now the main board is ready for removing.

So to remove the main board from the casing, lift the front
of the board and pull up and out to release the main board
from the holes at the back where the ethernet socket and the
display cable socket are slotted into the casing.

You should now have the main board free of the casing and
ready to work on!