GeForce 6 and 7 series in SLI mode unable to output interlaced signal.
NVIDIA has uncovered rendering problems and instability when outputting interlaced modes on the GeForce 6 and 7 series GPU when in SLI mode. Specifically, we uncovered issues with 480i, 576i and 1080i output over the Y Pr Pb component and DVI outputs. (The 480p, 576p, 720p, and 1080p progressive scan modes do not have problems in SLI mode.) This is a hardware limitation in SLI mode only and cannot be fixed via a driver update.
Due to this issue, starting in driver version 162.18 in Windows XP and 162.22 in Windows Vista, the driver will automatically disable SLI mode when using the 480i, 576i and 1080i modes over all connectors on the GeForce 6 and 7 series GPUs. The 480p, 576p, 720p, and 1080p modes are not affected by this change. To re-enable SLI mode, you must choose a non-interlaced output mode and reboot your computer.
This issue affects GeForce 6 and 7 series based graphics cards in SLI mode only (this includes the GeForce 7950 GX2 operating in multi-GPU mode). GeForce 8 series GPUs do not have this hardware limitation and users can output all HDTV interlaced and progressive scan outputs in SLI mode.