Really what I'd need is the size of the pipe and where you wanted to put it, but that's not all taht important.
Basically, you'd hold the pipe at an angle and Dremel off the bottom part of it straight. That way, the part that would be scraping the ground before is just flat (not realistic but no one's going to be looking at it from the bottom).
Then, in order to keep it from looking like a collection pipe (and more realistic, since real cars would ruin their mufflers by not doing this) cut part of the top off, so that it's flat in relation to the rear bumper.
See if any of this helps. I'm on AIM at
Maranello720R if you want to talk more directly.