My guess it you will need two graphics cards.
Reading up on dual link a bit:
- Max. res of a single link is 1920*1200 = 2.304.000
- Max. res of a dual link is (more or less) double that: 2560*1600 = 4.096.000
If you use two higher end (say 1680*1050) screens you'd already need 2*1680*1050 = 4.032.000, which should júst be doable. You will however need splitters which can let the DVI port believe it has two seperate screens, and I do not know if those exist.
Your second option would be a dual/triplehead2go of Matrox, but they will cost you a kidney, and probably someone else's too.
Last thing I can think of is a PCI graphics card. I heard (cannot confirm) it is possible to run a pci-e and pci card alongsides each other and run 3+ screens. Will have to check this with my own PCI card but I'll have to get it back from a friend first.
EDIT: something else, what about the PCI-e x1 slots? PCI-e is open ended so in theory you can put a very low end PCI-e x16 graphics card in there as long as it's just for office use. 2* HD3450 or 9300GT for example?