[chungy]

You might want to start with this guide: http://doomwiki.org/wiki/How_to_download_and_run_Doom

If you insist on using your CD rather than using a GOG or Steam copy, you'll want to be able to get at a "doom.wad" file. Depending on the CD you have, it'll either be available as a regular file, or compressed as an LHA archive. In the latter case, you'll find either one file such as "RESOURCE.1" which you can extract directly with lhasa, or several files like "DOOM_SE.1", "DOOM_SE.2", etc, in which you'll want to cat them all together into a new "DOOM_SE.lha" file and then extract that.