Unlike some other operating systems, Windows does not specify a default program that will execute to process unknown file types.Instead the Open With dialog starts asking you which program you wish to associate with the particular file type.
I don't know about you but I would find it much easier if unknown file types were to open in a text editor to allow me to see the content of the file. In many cases it is the content of such a file that is what I want to see. In others I find that looking at the content of the file helps me to work out which program that a data file expects to be used to open it so opening it first in an editor is convenient.
Fortunately, a minor edit to the registry will correct this for us. To start the registry editor select Run from the start menu and type regedit, then press OK.
You now need to go into HKEY_CLASSES_ROOT and scroll down until you find a key labelled Unknown. Within this is a sub-key called Shell.This in turn has one associated sub-key called openas. What you need to do is to add a second sub-key called open and within that create a further sub-key called command. Finally you set the default value for the command subkey to the command necessary to start your editor, for example to run notepad you add c:\windows\notepad.exe "%1".
An alternative to the above process is to use a .reg file to perform the update for you. This regnote.reg file will insert the necessary keys into Windows 98 or NT.
If you want a different program to run by default for unknown file types just substitute the command to execute the program that you want to run instead of c:\windows\notepad.exe.
This article written by Stephen Chapman, Felgall Pty Ltd.