Multi Monitors But Games Dont Recognize Both!

hello,

currently have two monitors, so i was never really interested in gaming with two since that would just screw my vision, but i about to get a 3rd and i thought i should just solve the problem now.

theyre both 19" and run at 1440x900, seems so clearcut and simple when ppl load up their CS and put in their dual monitor resolution then bam. i used to have an ATI card and was unable to do this. i currently have nVidia 8800gt and i wanna get this dualmonitor option down so i can do it with 3 monitors. what might i have to change/enable/disable(?) thanks!