So what we do, is to have notepad as an option in the Send-To options, of the right-click menu in explorer. It fulfils the purpose to perfection (atleast, in my case). Here's what we do:
1. right-click desktop, choose "New >> Shortcut"
2. Type the location of the item - "notepad" - (that's all, no need to give path)
3. Next >> type name for shortcut - "Edit with Notepad"
4. Click finish
5. Now right-click this shortcut on the desktop, and choose properties.
6. Confirm that the "target" and "start in" fields are using variables - "%windir%\system32\notepad.exe" - (absolute paths will be problematic if you use this .LNK on machines other than your own)
7. Now, browse to "%UserProfile%\SendTo" in explorer (which means "C:\Documents and Settings\User_Name\SendTo\" folder)
8. And copy the "Edit with Notepad.lnk" file which you already created, to that folder.
9. So now, you can right-click on ANY file-type, and be offered an option to open with notepad, from the SendTo sub-menu.
So now, you just right-click on an .nfo or .eml or .diz file (which are associated with other programs, and are sometimes just plain-text files), and choose "Send To >> Edit with Notepad" and it will open in notepad!
No more botheration of applying registry tweaks for something as simple as this.