http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supplyhttp://www.wikihow.com/Convert-a-Com...b-Power-Supply

This is one that I had been wanting to follow for a while but for some reasson couldnt find a spare PSU even though I have disposed of so many in the past.
Looks like a good tutorial.