Well first, you card needs to have sli with another card or have duel output. If you dont have those it WILL be laggy. Next, your reticual(SP?) will be split making the game harder. Now unless doom3 (I dont own the game so I wouldnt know) has settings for like 2000 by 750 (I dont know your resolution) the image will be severly stretched and look like crap. If it has this setting then you will nead to find the consol comands (usualy you put the word consol after the .exe in the shortcut) and then how to set it across two screens. I once did it with halo and put it in window mode through consol then stretched the window across my monitors....wasnt as fun as I hoped. Although worth a try.