how are you applying the textures to your parts?
a simple way is to simply drag and drop them from the material navigator list
*when you drag and drop a texture, make sure the part does not already have a material applyed to it, if so, use the material remover function in the tools section (warning - no undo)
then, depending on the shape of the part, the texture will look all weird, or even totally gray...
thats when the mapping part comes in

Gmax has some neat tutorials about mapping...
or you can look at
http://www.freeflightdesign.com/tutorials.html for some more FS focused tutorials
there