you should have ordered a video card that supports a dual monitor set up. just because it has all those ports doesn't mean it will support dual monitors. the dual monitor set up i had, used a dvi out going into a splitter and i was able to set it up in the display preferences. if you have questions about your machine, you should ask the people you're buyin it from, i'd assume they'd be the experts on thier products. you generallyl wanna ask questions like this before the purchase just to ensure you don't get disappointed with stuff you can use the way you'd like.
Trust me, I know what I'm talkin bout! check my history: