Unwrapping an object in different images

Is it possible to unwrap one object but in different maps? Or do I have to separate it in objects in order to accomplish that?

Yes, it is possible, just go into Face Select mode, and select the faces you want, then click “u” for unwrap… or you can go into edit mode, and edge select, then select several faces to… ok. i will just send you here…
http://otothecleaner.free.fr/tutorials/Gimpit/gimpit1/gimpit.html

Oops sorry… I double posted this…
I mean, make for example, an unwrap map of 256x512 for some faces and in the same object, make another map of 128x128 for other faces…?

i dont really think that this is the part of the forum for this question…it should go in texturing and lighting.