Here's a couple of resources:

Meguiar's engine detailing forum
Autopia.org's engine detailing DIY

I was taught never to steam clean an engine compartment by my uncle who owned a body shop for 40 years. You can pressure wash an engine with cold water, provided you wrap all electronics (distributors, fuse boxes, etc.) in shrink wrap. Hot water generates steam which in turn gets into electronics.

A good degreaser and an engine detailing spray is all you need to clean an engine compartment.