In our company we put up to 4, 6 or even 10 monitors to a single computer.
The actual solution is to go for Matrox DualHead, nVidia MuliView or other graphics cards with same specs.
Each card gives you room up to two screens which you can use simultaniously.
These cards also allow you to spread your taskbar across all the connected screens. (Which actually converts all connected screens to one single screen. -> resolution would be like "3096x1024" or even more.
Solution for your setup would be to buy one of these DualScreen cards and use the built in card for the third screen.
These cards don't cost that much nowadays and PNY / Matrox build these.
(My answer from http://superuser.com/questions/24376/three-monitors-setup-on-machine-with-integrated-graphic-card/24569#24569)
Though, I have tried a Matrox Graphics Card on a Windows 7 Machine and the driver support is pretty poor at the moment.
I would consider trying out a nVidia Quadro or a PNY - Yet I didn't have the opportunity to try these out on my Windows 7 Machine..