"Freestyle" was the code-name for the Media Center variant for Longhorn (It was also the code-name for the Media Center variant of Windows XP, as that was also still in development at the time). Freestyle would have made use of major Longhorn technologies, like Avalon and would have been integrated into its exclusive applications, such as MyTVApp. While a Freestyle variant does exist for most early Milestone 3 Longhorn builds, this SKU cannot be accessed by default, as one would need to convert a supported installed Longhorn build by following the guide below.
Converting to Freestyle
The process for converting a Longhorn build to the Freestyle SKU is quite simple:
First, install your Longhorn build
Go to Control Panel
Click Add/Remove Programs
Click "Freestyle"
When Setup asks for the installation disk, be sure to point to X:\I386 on the .iso or disk.
Restart.
A picture of the Freestyle bootscreen
Supported builds
3683
3706
3713
3718