I've also decided to use an ATX power supply to power the whole thing, I had 300watt supply spare and its capable of supplying 18A on the 12v rail which is 2 more than suggested on the reprap wiki. I followed this page on the wiki to modify it for use as a power supply for the machine.
On the inside I nstalled a switch that turns the power supply on and off trimmed all the wires off the usual mother board 24 pin connector, the big white thing near the fan is a load resistor on the 5v line which is recommended on the wiki to stop the supply from tripping out.
Here's the finished supply everything appears to work after testing, in this picture you can see I left one string of molex connectors on in order to power some fans which I may use for cooling the parts as they are printed. You can also see the fuses I added after a suggestion by a friendly Jaycar dude, on the two twelve volt lines that I am using to power the electronics.
