Scrolling heightmap

Hi, I am developing a game similar to Raptor, fly-shot-em-up-until-u-are-dead. But instead of doing the traditional 2D style I want to do it more or less in 3D. So what I have in mind is to make a heightmap (or similar) as ground. Obviously I can''t make an neverending heightmap so I need to scroll it somehow. And that, folks, is my question. How to scroll a heightmap, and is there something I should think extra about etc? Thanks, Bauer. CUselessStuff::NiftyQuote();