Put them both in the slots, plug in the power cables, and connect the bridge and connect your monitor to the 1st card (preferably, but it doesn't really matter). Boot to Windows and install the latest driver. Then go to the NV Control Panel and be sure that "Maximize 3D Performance" is ticked in 3D Settings/Configure SLI, Surround, PhysX.
Windows may load a driver from its cab files and ask you to reboot. If so, let it and then load/run the latest driver from the geforce.com web site.