I have installed such a system for a client using a Matrox dual head Graphics card - the one I used has been superseded by this one:
http://www.matrox.com/mga/products/m...eries/p650.cfm
You can also get one with triple head, for future proofing:
http://www.matrox.com/mga/products/m...eries/p750.cfm
If you haven't got DVI they come with converters to the standard format.
Not good for gaming though only 64Mb on board + you need an AGP 3 compliant system. If you need more memory on board they are other products from Matrox - see the first few here:
http://www.matrox.com/mga/products/home.cfm
hth
Charles