Windows XP introduced a new features for configuring the file association for unknown file types.
When trying to open a file which Windows doesn't recognize, then it will present you with two options:
- Use the Web service to find the appropriate program
- Select the program from a list
The Web service redirects one to ex. http://shell.windows.com/fileassoc/0409/xml/redir.asp?Ext=rar
which presents different options for opening the file. One might get annoyed by this extra dialog, and it is possible to disable it.
[HKEY_CURRENT_USER \Software \Microsoft \Windows \CurrentVersion \Explorer]
InternetOpenWith = 0
[HKEY_LOCAL_MACHINE \Software \Microsoft \Windows \CurrentVersion \Policies \System]
NoInternetOpenWith = 1
More Info MS Technet: File Association Web Service