Guide: Check his qualifications. If he's a member of the BMG, then do it through them, and he can be trusted. Other than that, ask for phone numbers, of his previous clients, and phone them to see what he was like.
Route: I am going to Monty Bloncky (as we call it) summer 2003 all being well, and we're taking the normal route (Gouter Route). There are websites like the BMC's which have details about the mountian, and routes as well as guides. Also Google search for "Mont Blanc" (inc quote marks). Also look for my thread in this thread titled Mont Blanc. There's a few people's accounts of their experiences.
Take a look.