I got a comment from a customer asking about the availability of some Windows features such as Internet Explorer and Windows Media Player on a Windows XP Media Center 2005 computer that they purchased from an OEM. This comment made me realize that it is likely that not everyone out there is aware of a control panel applet called Set Program Access and Defaults (or SPAD for short) that can be used in Windows 2000 and Windows XP to control the default behavior of the OS for certain types of middleware applications such as email clients, web browsers, media players, instant messaging clients, etc. The SPAD applet also has specific items that can be used to show or hide individual Media Center experiences (DVDs, music, radio, TV, videos and Online Spotlight).
If you are interested in taking a look at the SPAD applet, you can get to it by opening the Add or Remove Programs control panel on a Windows 2000 Professional, Windows XP, Media Center or Tablet PC OS. There should be an item on the left side of the Add or Remove Programs control panel called Set Program Access and Defaults. Clicking this will open the configuration window for SPAD. You can use this to specify default programs to use for various activities and also enable or disable access to programs. A common usage of SPAD is to hide all entry points to Internet Explorer or Windows Media Player for example.
If you look at the Custom settings for the SPAD configuration control panel on a Windows XP Media Center 2005 machine, it looks like the following:
Applications that fit into the categories in the SPAD configuration control panel can install registry keys that will cause their applications to appear in this control panel if they want to. The registry values that control what appears in the SPAD control panel are located at HKEY_LOCAL_MACHINE\Software\Clients, and there is some good documentation regarding how to register an application to work correctly with the SPAD control panel in this MSDN article if you are interested.
There is also some more in-depth information about the SPAD control panel in this article.