got a link to the cnc how to?If someone else wants to do this; it's a good project but there's only one _big_ pothole you don't want to fall in.
"AT" power supplies are the easiest to convert, although they pull less amps, but don't have the pitfall.
"ATX" power supplies can pull more amps on the 12V rail, but some power supplies have 2 12V rails (like one that's good up to 8A and the other that can pull up to 16A; it's written on the power supply itself). Just don't solder the wires from both rails together or you can get a nice smoke show.
If you want to convert an ATX power supply that's laying around, I suggest you do like me and read this throughout. It's a great little howto.
Now I got to follow another howto and convert my lathe/mill combo to CNC :drool: