Rendering DEM

Dear friends,
I have rendered a terrain based on RAW file which gives me the height information. Now I want to render a terrain based on a USGS Degital Elevation Model. I have a (.DEM)file of a perticular area (downloaded from net). The Advantage is that i ll get lat-long infos from DEMs, but i have no idea about (.DEM) file structure. Is there any parsing code available for DEM? Wait for any help.

With lot of thanks in advance.

Try this site, it specializes in this kind of thing and your question is not directly related to OpenGL.