I believe it's asking for the Doom CD. The linux version requires you to have some of the proprietary software from the original Doom game.
Once I got legacy doom working. Legacy Doom required some *.wad files from the original game which I didn't have. In the end I got the *.wad files from a completely free version of doom. Can't remember the details.
But my point is that it's all possible.
vxc
p.s:Have you tried the latest Unreal Tournament Demo! Thats the only game I play on my PC and it works great. Love the multiplayer.