"yes it can, but when you decide to play a game you're stuck with one monitor. "
That one should be a two.
You can get another card to sli with it or get another card without sli to use for display, but of course, without sli, you cannot combined the graphic processing power of both card. Otherwise, you can consider selling yuor card and get one from AMD instead. A 6870 will have similar performance to the gtx460, but you don't get cuda and physx.
If i get a 6870, do I have to get a monitor that has a display port input or can I just get away with using HDMI and DVI connections for all three monitors? I do have a DVI-VGA adapter that I use for my second monitor since it's an older one. My primary monitor is connected by a HDMI cable.