All you need to do is un-install your current VGA drivers,shut the system down,remove the current card(if not one of the 7900s).Then install bothe 7900,make sure all the necessary power connections are connected,connect the SLI bridge connecting the cards together.Connect your monitor cable and turn the machine on.Windows will try to install drivers,but just click cancel on bothe windows.(when two cards are installed,windows will see them seperately).At this point,you disconnect your internet connect,and shut off your anti-virus program.Now I'm assuming you've gone to NVIDIAs website and downloaded the latest drivers.You install the drivers,reboot the computer,and voila,you now have SLI.Not all games will take advantage of SLI.You may even have issues with some of the older games.But although I don't currently run SLI,I have done so in the past and was very happy over all with the performance increase I got.Goodluck.
Dahak
M2N32-SLI DELUXE WE
X2 5600+ STOCK (2.8GHZ)
2X1GIG DDR2 800 IN DC MODE
TOUGHPOWER 850WATT PSU
EVGA 8800GT SUPERCLOCKED
SMILIDON RAIDMAX GAMING CASE
ACER 22IN WS LCD 1680X1050
250GIG HD/320GIG HD
G5 GAMING MOUSE
LOGITECH Z-5500 5.1 SURROUND SYSTEM
500WATS CONTINUOUS,1000 PEAK
WIN XP MCE SP2
3DMARK05 15,686
3DMARK06 10,588