JoT, check out the rear of your motherboard, in one of the corners, there will be some lettering, indicating your board's PCB revision. Here's an example:
http://www.ocforums.com/attachment.php?attachmentid=37375&stc=1
If your board is a "REV 0.52" (the newest one), then you can simply solder a wire between the two points (VTT=VREF) shown in the picture that you linked in your first post - really easy
. You'll also want to check the VTT voltage at several different VDIMM settings with a multimeter afterwards, to make sure that it worked properly.
Check out this thread - it contains a lot of information on the VTT voltage modification (even though it starts off on another topic) - read the whole thing or it won't make sense
:
http://www.ocforums.com/showthread.php?t=337005&page=2&pp=30&highlight=VTT
If you do have a "REV 0.51" board, you need to use the trace cut method. I haven't done this mod personally, but it looks fairly easy, although it will be time-consuming and annoying to have to adjust VTT on-the-fly.
http://www.malvescorner.com/images/nf7vbt.jpg
Basically, you cut the trace shown in the picture, using a razor blade. Then, you polish both ends of the cut trace lightly and carefully untill you can see the metal underneath the coating on the PCB. You can solder your leads onto these metal patches, and run them to your potentiometer, as shown in the picture.
Lastly, you solder your potentiometer (set to 0 Ohms resistance to start with - use a multimeter to check it) to your leads, and fire up your machine. Because you use a VR with this method, you need to adjust it on-the-fly to match your VDIMM voltage. So, crack out your multimeter, and adjust the VR's resistance untill your VTT matches exactly 1/2 of your VDIMM, which you can use as a reference voltage to set your VTT. You'll probably need to check your VDIMM with a multimeter as well, to avoid software monitering from fubaring your numbers.
Good luck, if you have any more questions, or need clarification, don't hesitate to ask.