As previously mentioned the only problem with Freeview HD in Windows Media Center is the missing guide data for the HD channels. There are four channels missing guide data: BBC 1 HD, ITV1 HD, Channel 4 HD and the BBC HD channel.
The first 3 are easy to sort out which is documented bellow but for the BBC HD channel there is no guide data available via Media Center so to get the guide data working I have developed a small program that will download the EPG data and then import it in to Windows Media Center.
To use the application you will need to download and unzip the xmltv tool, this is an open source application for download EPG data. My application configures and make use of this service to get the EPG data, it then converts it to a Windows Media Center compatible format and loads it into Media Center. There is also an option to schedule the download to update the EPG daily
You can download xmltv from here, once you have download it extract the zip file to the local machine (I would recommend Documents\xmltv) and then install the application which you can download from MadeforMediaCenter.com
EDIT You can also get xmltv in a setup file
In a future build it will also download the other HD channels guide data but for now see bellow for to get their EPG data setup
Setting up BBC 1 HD, ITV1 HD, Channel 4 HD
Setting up the missing data is pretty easy, you just tell Windows Media Center to use the guide data for the standard channels
Load Windows Media Center and go to Tasks, Settings, TV, Guide and Edit Channels
Select the the channel eg BBC 1 HD, select Edit Listings
Select the normal SD channel eg BBC 1
Select Copy listings
Click Save and you can make sure its labeled correctly eg BBC 1 HD
So that will get the 3 channels sorted and my BBC HD channel will fix the other, you will then have a complete Freeview HD Media Center System