Manually: regedit and navigate to
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\*\Shell
add the key "notepad"
it's default value should be "Open with Notepad"
now, under "notepad", add the key "Command"
it's default value should be (with the quotes) "C:\Windows\System32\Notepad.exe" "%1"
ok, exit regedit and go right click on ANY file...
your new option: Open with Notepad