I believe terkan is correct. Most (all?) cards with 2x DVI and 1x HDMI will still only allow 2 monitors max.
I believe the exception to this is if the card has 2x DVI or HDMI and 1x Display Port; if a card has that, then it should be able to run 3 monitors, but you need a Display Port compatible monitor, or a Display Port -> hdmi/dvi adapter, which are pricey.
You could also try something like tihs:
http://www.techspot.com/news/38426-a...efinity-6.html
But again, you need the display port adapters..
The sure way would be to run 3 video cards.