Gtk-WARNING **: cannot open display:
Hi. I'm starting out with linux. I have installed archlinux 0.8 (voodoo), base system, on an AMD 64 machine. I configured network and internet connections, updated packages and all went well. Then I used pacman to download and install firefox. That seemed to go well too except for the fact that firefox does not run. When I try to start it I get a warning message that says "Gtk-WARNING **: cannot open display:" and the program doesn't start.
I've looked all over and can't find a good hint at a solution.