personally i have built a few maxim based diode readers ...
suggested ics are maxim max6657/6658/6659 series ..
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578
if you want to use the internal diode on a board that already has a diode reader use desoldering braid (correct term?) on the dxp/dxn pins of your motherboards temp management ic to remove as much solder as possible ... then put a razor blade under the pin and bend it up just a very little.. only so much that the connection is gone .. now solder your wires to the back of you mobo cpu socket... very easy to undo ...