With Windows 7 you can still access your Netflix instant queue and watch movies and shows. The two applications I have tested on Windows 7 are MyNetflix and vmcNetFlix (the download link is towards the bottom, right above the release notes for vmcNetFlix). Both worked. With MyNetflix I never figured out how to make the playback go fullscreen without using a mouse. I don't like to have to use a mouse (I don't even have one connected). With vmcNetFlix you can make it go fullscreen once it starts playing by hitting the Play button on your remote. There may be a way to make it go fullscreen without a mouse when using MyNetflix but I have not found it.
Once you install the app you will find it in the Extras section on your Media Center.
You'll have to switch to the SilverLight player to watch Netflix content on your Win7 Media Center computer. To do this perform the opt-in at the Netflix site:
You can read about it here: