If you want a "dummy door" you may want to put a sheet of doorskin up and use it as a jig, never done this however I have heard of it being done.
another way would be to get a helper and place the door in the opening, marking where it may need to be cut/planed, as well where hinges would go.
Usually when hanging doors in an existing frame, I will check the doorframe for level/plumb and measure then cut out hinges, hang the door, pack out a hinge if necessary, or cut/plane door if necessary. You can always adjust the frame if it is out of whack considerably (as mentioned above), rather than trying to make your door fit into it. Just keep in mind you will have to remove and re-fasten the trim to move the jamb.
Another option would be to go pre-hung, nice and fast to install, especially if your frame has old mortises cut into the strike jamb.
Last edited by chrisbc; 10-17-2011 at 12:27 AM.