I haven't looked into building in a while, so I'm not up on exact parts.
But you'll probably only need an AMD processor (they have a lot of good stuff aimed towards the low end), minimum of 2Gb of RAM (although I highly doubt you'd need more than 4Gb for your purposes).
As Sigz said, you'll need a graphics card for two monitors, but it won't need to be anything high end (any old Gforce will probably have dual DVI).