Youve downloaded the software for the PC?.
Heres how its done:-
View Video from a PC running Windows XP or Windows Vista
When you connect your Xbox 360 console to a PC running Windows XP or Windows Vista, you'll see all available video content listed on the Video screen in the Media area of the Xbox Dashboard.
To view video content from a PC running Windows XP or Windows Vista
1. Visit
www.xbox.com/pcsetup to download and install the appropriate software for your PC. For more info about setting up your connection, see Share Media from a PC with Xbox 360.
2. After you've installed the software, make sure your Xbox 360 console is connected to your PC using one of the following:
* A standard Ethernet cable (sold separately for the Xbox 360 Arcade System).
* The Xbox 360 Wireless Networking Adapter.
If your console already shares a router with your PC for Xbox LIVE access, your PC is effectively already connected your console. Please be aware, however, that wireless streaming between your PC and your console requires an 802.11a network connection, which is faster than the 802.11b and 802.11g standards.
To learn about home networking, see Home Networking Basics.
3. Turn on your Xbox 360 console and go to the Media area of the Xbox Dashboard.
4. Select Video. If your PC is not selected, press X and select it.
5. Select the file you want to view.