I know this is an old topic but seeing as it hasnt been resolved yet, couldnt you take the old psu you had from the shuttle, cut it off and then attach that to a normal atx psu, assuming that it has the same 3.3v, 5v, 12v and on cable? Even if colouring is different I'm sure you could find a diagram to compare the two? After a little googling I couldnt find a diagram of the connector for the shuttle psu, but perhaps you have the colour codes of the wires on the side of the shuttle psu?
Edit:
I am aware that this is a stupid, stupid idea, just remeber it comes from someone who has unlocked a cpu and mobo by soldering on them

and had his water cooling running off a mains water supply for a while.
<quote>I don't think so, considering the power requirements and outputs are totally different.</quote>
Just for my interest what are they?