You need a 1" threaded headset. You can spend anywhere from $10 to (probably) $150 or more on a really fancy one. A $20 one is all you need.

On a 21 year old carbon frame, unless you have the PROPER tools to do this I would highly recommend having a competent shop do it. And I'm usually one to recommend doing everything yourself. A pressed in headset needs to be hammered out and a new one needs to be pressed in. If you do it wrong, you can easily ruin your frame.