most times when you're trying to make sure your 3 planes all line up you're doing it in photoshop... this way you've got ruler tools and such that you can line up lines with, etc. if you go to www.learningmaya.com and look at the modeling page, there's a tut about a car, and the whole first section or two deal just with aligning the images to make sure they match when imported to image planes in maya... take a look.