SLI ?? CROSSFIRE?? HELP NEEDED

anyone have any idea about sli or crossfire??? im a newbe. i have at present a gforce 9800gt xxx it says its sli ready i also have a second one in a cuboard, whats the benifit of sticking them both in? is it just a case of putting them in and thats it or is it a pain to set up? my board gigabyte ma790x-ds4 says Dual PCI-E 2.0 x16 graphics interfaces with ATI CrossFireX™ support for extreme gaming performan. does that mean i can just insert these 2 cards together and thats it? and info would be excellent

SLI can only be used with a Nvidia chipset equipped board. You have a AMD chipset board which can be used for crossfire. Each board will accept and use a single Nvidia or AMD graphic card. HD4870x2, 4850x2, GTX295 count as a single card and crossfire or SLI is not needed. Your 9800GT will work fine in your 790X board, but you cannot SLI another one.

Im seeing alot of these post's i have recently Purchased another ATI 4850 TOP to run crossfire, well i was dumb and didnt do my research /slap me I currently have an ASUS M2N-SLI from my build about 2 months ago, well come to find out my board does not support Crossfire, but does support SLI, I was wondering if anyone in this type of situation AKA you have NVIDIA cards but a Crossfire ready Mobo, if anyone is willing to do a Trade let me know ill create a TomsHardware profile also my email is thesr5@gmail (dot) com. Let me know if anyone is interested.