It's unlikely that you'll be able to play TDM without a copy of Doom 3 for the foreseeable future. TDM reuses a number of Doom 3 assets and those are not included with the open source release of the engine.

(If you don't know, the Dark Mod is a Doom3 total conversion inspired by the Thief series, one of my all-time favorite games).

Me too! I just heard about the dark mod a while back and tried to get it working. I didn't want to go buy Doom3, because I don't like the game and I couldn't be sure whether or not TDM would work. So I tried with a pirated version and it didn't, so I'm stuck waiting for the open source release of D3 engine (and the subsequent "porting" of TDM).

(For some reason, PC games for me have a terrible track record of not working. I often try a pirated version of the game and if it works and I like it, I might buy it. If the pirated version doesn't work, I won't bother because experience tells me the legal one isn't probably better and I hate begging for refunds from Steam support).

You can buy Doom 3 on Steam for 20 bucks. Or if you wait a few weeks there's usually Holiday Sales on Steam, you'll probably be able to buy it for 5 or 10 bucks.

http://store.steampowered.com/app/9050/