I did wonder about this and Ian has just reported on his blog here that the newly released version 1.0 of the MCE Sideshow gadgets still does not work on the TV Pack version of Media Center, which is a real shame.
To get the Media Center Sideshow gadget working on TV Pack you can change a setting in the registry, edit the registry at your own risk!
1. Go to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Media Center
2. Change the Ident version to 5.0 from 5.1
3. Run the Sideshow install
4. Change the Ident value back to 5.1
There is also another way to get the MCE SideShow gadgets installed on a TV Pack version of MCE, you need to modify the MSI files in a certain way and then they can be installed as normal. This has been tested and works, however you might as well just use the reg edit work around shown above instead.