hmm pretty sure you can. ive got doom bfg and ive been able to do it. but you cant play them from the steam client itself. you have to use a source port like gzdoom to run it tho. you just need the iwads from doom1 and 2, and then copy/paste them to the gzdoom folder or something. sorry haven played it in a few months so forgot exact steps. --- Posting from phone. So Police, don't whine about minor mistakes.
Yeah, just install it and pull out the Doom & Doom2 .wad files and run them with either GZDoom or Zandronum for BD. --- http://www.steamcommunity.com/id/daylecman Phenom II X6 1075T @ 3.5GHz - 4GB DDR3 - 120GB SSD - GTX 460 1GB - Blackwidow Ultimate