You could try to copy the registry file in that first link and merge it into your Registry.
Copy this -
Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT\txtfile\shell]
@=""
[HKEY_CLASSES_ROOT\txtfile\shell\open]
[HKEY_CLASSES_ROOT\txtfile\shell\open\command]
@="NOTEPAD.EXE %1"
[HKEY_CLASSES_ROOT\txtfile\shell\open\ddeexec]
[HKEY_CLASSES_ROOT\txtfile\shell\open\ddeexec\Application]
@="NOTEPAD"
[HKEY_CLASSES_ROOT\txtfile\shell\open\ddeexec\Topic]
@="System"
[HKEY_CLASSES_ROOT\txtfile\shell\print]
[HKEY_CLASSES_ROOT\txtfile\shell\print\command]
@=hex(2):25,00,53,00,79,00,73,00,74,00,65,00,6d,00,52,00,6f,00,6f,00,74,00,25,\
00,5c,00,73,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,4e,00,4f,00,\
54,00,45,00,50,00,41,00,44,00,2e,00,45,00,58,00,45,00,20,00,2f,00,70,00,20,\
00,25,00,31,00,00,00
You will have to save it as a .reg file via Notepad and then double click on the saved file.
Launch RegEdit and use the Help program as it is your best source of information about RegEdit.
These following links take the subject a bit further too.
310516 - How To Add, Modify, or Delete Registry Subkeys and Values by Using a Registration Entries (.reg) File
310426 - How To Use the Windows XP and Windows Server 2003 Registry Editor Features
I remember the first time I looked at the Registry and how daunting it all seemed, but with time and plenty of safety nets (see below) it soon becomes as familiar as using Explorer.
If you change a key or value, use the Export function to save a copy of any key prior to your change. You just right-click on the highlighted key to find Export.
To backup the whole Registry for easy re-installation (even from other operating systems or DOS) I recommend this free program.
Registry Backup and Restore for Windows NT/2000/XP