Go to JoAnn fabrics. They carry headliner material and the adhesive needed. I paid 40 to redo the one in my sentra and it looked original when it was done. To answer your other question yes you do have to remove the old material. The one in my old sentra was real easy to remove. I'm betting that the one in my 98 will be a lot harder. Just take your time and make sure you get all of it off. When you put the mew material on do it in small sections and do it slowly and make sure that you get it in all of the grooves.
1998 Ford Ranger XL regular cab longbed Oxford White Air box mod, XLT third brake light with cargo lights, Exploder dome light, Euro 93-97 taillights, Clear corner lights, Clear headlights, Ranger splash color matched power mirrors, 97 XLT non-power door panels, Exploder radio bezel, Exploder Sport gauges, Exploder power cloth seats, Chrome tailgate handle, 06 Ranger XLT badges, Chrome XLT front grill, 01 4X4 XLT chrome bumper with egde lower valance, auto-dim mirror, overhead console, Exploder dual sunvisors Exploder full length center console, 01 4WD teardrop rims with 245/50/16 tires