All Slingbox's are compatible with Windows 8. But you have to be in Desktop Mode, not the Metro mode on the computer.
The computer also cannot be a Surface Windows 8 RT, but with the Slingbox 350 you can take advantage of the SlingPlayer for Windows application that places a Desktop icon in your Metro mode that will allow you to watch the Slingbox. Keep in mind this is an application you have to purchase from the Windows Market Place.
Hope this helps!!!
Sling Media Moderation Team