1.d4 d5 2.c4 Nf6 is the Marshall Defence, which you are correct in considering poor for Black. I started up a thread about it a long time ago (in fact, just after I joined chess.com) which got a bit out of hand, but you can check it out here for some useful tidbits: http://www.chess.com/forum/view/chess-openings/marshall-defense
However, the line you played (i.e. an immediate 4.e4) supposedly allows Black to equalize with 4. ...Nf6 5.Nc3 (more or less forced, to defend the pawn) followed by 5. e5!, striking back at the centre and intending 6.dxe5 Qxd1+ 7.Kxd1 Ng4. But a bit of analysis I did on my own makes me think White still holds an advantage in that position...I'm not sure though. The "usual" response for White if Black chooses to play the Marshall Defence is supposedly 4.Nf3 followed by 5.Qb3; which also leaves White with a clear edge. I never really saw the problem with 4.e4 though.
Sorry for the rhyme, I just couldn't help it :p
Anyway, I've played chess off and on since I was in secondary school, but since it was never for any length of time (a few games here or there), so any advice would be great!
Also, I was wondering how viable that Nf6 is in the opening line 1.d4...d5 2.c4...Nf6. It seems like it just positionally screws over black...