Re: Quad Monitor graphics card
You can use any of ATi's Eyefinity Edition cards, these support up to 6 monitors using Mini DisplayPort connectors (or active adapters). You can also put two cards in CrossFire (ATi's 5xxx cards support up to 3 monitors except for the very basic ones, with two of them in CrossFire you can have 6 monitors, the Eyefinity Edition cards have 6 monitor support instead of 3, so two of these supports 12 monitors, etc..).
Eyefinity allows you to either use the displays individually or map them into one super-huge monitor that you can render programs and games across. To use the Eyefinity group modes you need monitors with equal resolution, but for individual monitors they can be different.
My regular 5870 supports 3 monitors, I'm using 3 Dell ST2210's and it works nicely. I had to use a DisplayPort to VGA adapter on the third monitor but it looks just as good as the DVI ones.