As we know Media Center is no longer an integral part of Windows 8 and will be delivered as an Add-on to Windows 8 for few bucks.
Microsoft has also ripped of Windows Media Center from Windows 8 Release Preview. If you want to use Windows Media Center, you need to add it by following these steps:
- Swipe in from the right edge of the screen, and then tap Search.
(If you’re using a mouse, point to the upper-right corner of the screen, and then click Search.)
- Enter add features in the search box, and then tap or click Add features to Windows 8.
- Tap or click I already have a product key.
- Enter this product key: MBFBV-W3DP2-2MVKN-PJCQD-KKTF7 and then click Next.
- Select the checkbox to accept the license terms and then click Add features.
- Your PC will restart and Windows Media Center will now be on your PC and the tile will be pinned to the Start screen.
Source: Windows 8 FAQs