Illustrator is a Vector based program and doesn't print a background unless you make one in the artwork. The great thing about it is that, unlike photoshop, you can get sharp edges no matter how you resize the art.... I could explain more, but this link will be much more helpful
FYI: it's about decals and part of it is about making your own
http://www.childofmecha.com/Modeling...ls_Demyst.html