Great question, yes you can map different areas of a model with different mapping modes.

Some forthought while modeling can help here but assign different material names to each area or group of polygons that require a different mapping approach, that way you can easily seperate them in your mapping program. First of all I highly recommend "Lithunwrap" its a free download. I started out using uv mapper like everyone else, then found lithunwrap, never looked back. Yes its a pain in the ass to learn yet another program but lithunwrap is easy and vastly superior to uv mapper (in my opinion )

Mapping is sort of like solving a puzzle, becoming proficient at it will greatly inhance your models and the quality of your work. Box mapping is usually the best for most situations, decal is good for flat surfaces, and of course cylindrical for cylinders. I dont think planar is good for anything, I dont even know why they invented it, its useless. When modeling picture in your mind how you are going to apply textures to differnt parts. dont be affraid to break a model up into many material zones if it helps with applying textures. I do most of my texturing in photoshop but there are times when zbrush really comes in handy for this.