This site (
http://paras.rasmatazz.bei.t-online.de/) should pretty much sort you out.
Or, if you want to do it the easy way, download the nero image (
http://prdownloads.sourceforge.net/scummvm/scummvm-0.4.1-dreamcast-nero.zip?download) and burn it using Nero Burning Rom (Shame on you if you don't have it, you'll find a 30 day trial here (
http://download.com.com/3000-2646-10211579.html?tag=lst-0-1)).
Once you've burned the image to disc, simply stick it in your Dreamcast, let it load up and then either swap the disc for the game of your choice, or mess about with the demos that are included.
Be warned, though - It's a little stuttery on the Dreamcast, and some games may refuse to work.