OK. Would that work with my current graphics card so I can plug two moniters into the ati card and 1 in the Nvidia?
As a general rule of thumb, don't mix ATI and nVidia in a single system unless you really know what you're doing, or expect to sit and troubleshoot with custom drivers for a while.
A single eyefinity card from ATI will drive 3 displays from a single card (I think one needs to either accept a DisplayPort input or you'll need a DisplayPort adapter), while any nVidia card will drive 2 monitors. If you already have an nVidia card, you should be able to buy a cheap second which you can add in to drive the 3rd display.
I'd recommend something from the lower end GeForce 200 series (GT 220?), but any nVidia card should do - your local computer parts outlet should have one for $25ish if budget is really a limiting factor.