Are all rims the same or is there a certain type of rim for offroading?
So long as you can mount your tire on it, a rim is pretty much a rim. Some Jeepers prefer to run steel wheels as they are typically much more affordable, are easy to touch up and will bend as oppsed to breaking but, they also tend to be heavier than aluminum. The one thing I would recommend is that you try and get a rim that is about 8″ in width. The narrower width will help keep your tires from loosing a bead when aired down for the trail.