There was a chap who used to post here a lot, Brian Calvert and 4-5 years ago he started his own site called project guitar as kshands mentioned below.
http://www.projectguitar.com
He's got a bunch of tutorials on there so see if you can find anything there.
Also I'd advise you to just try and stick bunch of glossy magazine pages on planks of wood just testing and stuff and clear them and see if it works before you try and actual print on a guitar.