The general idea is to make your (for example) side view a convenient size (assume you use 100 pixels per meter, so a 5 meter long plane will have a 500pixel wide image (let's say it's 5m wide by 2m tall, so you end up with a scaled 500 x 200 pixel image.
In gmax, you create a 5m x 2m plane, and apply your 500p x 200p image as it's material.
Repeat for any other views you may have, position the planes correctly, and then freeze them in place (remember to uncheck 'view frozen in grey' in the properties)
There are better tutorials on this at FFDS -
http://www.freeflightdesign.com