Headliners are kinda easy to replace, it's basicly cardboard with a foam-backed cloth covering held in with a few clips. The cloth can be found at almost any fabric shop -- maybe even Wally-Mart. To remove the liner usually its just a matter of taking off the ruber around the door trims, the plastic A and B pillar trims (maybe even C), the interior light, and the sunvisors. Some have an upper console that will need to be removed as well. Once all the trim is gone, there may be a few clips that hold the liner up. Many times the liner is installed before the glass durring assembly line production thus making removal of the headliner assembly out a door quite an experience. Once out though (or inside with the trim removed) pull off the cloth, apply spray glue (3M 77), and starting in the center working outwards, apply the new fabric. Trim the edges and reverse the procedures putting it all back together.
Or, you could go to a local upholstry shop and let them do it, it usally runs in the $250 range.
