I just set up a Dell XPS with the Sapphire 4850x2 (quad-output). I'm running four screens at 1920X1080 each

When you get the card, go into the Catalyst Control Center and uncheck the enable Crossfire box. We spent freakin 30 minutes trying to troubleshoot why the card could only show two outputs. Turns out the Crossfire is enabled by default, DOH.