I'm not 100% sure as it's not something I have done myself, but go in to your BIOS and in the Advanced Chipset section, there should be a "Hybrid Support" title. Set this to Auto, and make sure the onboard graphic card is enabled.
If you want to use Hybrid Power to save electricity, then connect your monitor to the onboard graphics card, so when you aren't playing games, the main graphic card will power down while you use the onboard one. If you aren't bothered about this, then just plug it in to your 9800.
When you now boot in to Windows, there should be an Nvidia icon asking what mode you want to use. "Boost Performance" is most likely what you want to use.