Tipster Larry B. pointed us to the above video, uploaded today, showing how installing games to your 360 hard drive will work. The process produces faster load times for you, but you still need to put the game in the tray (see the end of the video) to satisfy DRM protection.
Video in link shows HDD installation for GTA IV, which should be great for reducing load times. And it appears it installs the full thing to HDD, and you only need to insert the disc for copy protection reasons. Now we know why MS decided to upgrade the HDD to a larger size.