There is no native Netflix app (yet), so you’ll have to watch it through Windows Media Center.
1) Add the Windows Media Center Feature (http://news.cnet.com/8301-10805_3-57445533-75/how-to-add-media-center-to-windows-8-release-preview/)
2) Run the Netflix app in WMC
3) Install Silverlight when prompted
4) Close WMC (so Silverlight will finish installing)
5) Open WMC >> Netflix. Enjoy!