I use Blockbuster, not Netflix, but this looks like a great Media Center plug-in:
If you're a Netflix subscriber, you definitely going to want Andrew Park's new plug-in for the Vista version of Windows Media Center called MyNetflix. The plug-in lets link up to your Netflix account, view your queue, browse for movies, add movies to your queue, and, of course, watch movies! Using Netflix's streaming service, you can watch movies immediately, without having to wait for discs to come in the mail. Because the plugin relies on certain software in order to work, this only works on Media Center PCs, not extenders (like the Xbox 360) unless you have your PC hooked directly to your TV or have a Netflix "Watch-Now" enabled set top box, which will be out later this year. The plugin is in beta and is available for download here.