If you have Nvidia hardware in your PC (and Steam installed), you can go to this page, click the "Get it Now" link and run the scanning software. It will look for Nvidia "hardware" (Just cards or motherboards too?) and if it finds the Nvidia stuff it will allow you to download a delicious taste of the Valve smash hit, Portal. Apparently there will be a link included in Nvidia drivers in the future as well. I wonder how long this will be available though. It only says "for a limited time".
"More Steam gamers, including myself, play on NVIDIA hardware than any other GPU," said Doug Lombardi, vice president of marketing at Valve. "That's a testament to the company's long history of innovation and quality. By working together with NVIDIA to expand our development, distribution, and marketing efforts, we're increasing our ability to serve the millions of NVIDIA customers logging onto Steam and help us prepare for our next generation of content."
"Valve's endorsement of our technology and tools is yet another example of how the world's leading gaming companies are working with NVIDIA," said Roy Taylor, vice president of content relations at NVIDIA. "Portal is the hottest new, award-winning title from Valve, and we're delighted that Valve will offer First Slice exclusively to GeForce customers."
Portal is very fun you guys. I have played it all the way through and I also completed all the advanced levels. It won Joystiq's game of the year award and it is only about three hours long. Other awards it got this year include: