I was really surprised to see this after I had gotten this reply from HiRezStew when I inquired about Eyefinity some time ago : http://forum.globalagendagame.com/phpbb/viewtopic.php?f=149&t=8906 (requires beta access)
The /setres command Zypher indicated will "work" in the sense that it will change your resolution to the indicated dimensions. But the specific multiple-monitor configuration is not tested or officially supported at the moment, and thus I would expect some things to potentially not work, and other things to work but potentially be awkward. From light, unofficial testing, it generally looks like the Combat missions will be largely fine, but you may see some problems in a few other areas (such as character creation).
-Stew
Though, when I got in game, it was very much the opposite, character creation was fine, combat was unplayable.. :-| Go figure.
I hope HiRez pulls their head out of their asses and gets around to supporting this, I had been looking forward to this game for a really long time..