Sorry for the delay in getting back to you.
Did you perhaps try the automated "Fix It For You" link in the article, I believe it contains the actual registry key (HKEY_Local_Machine\Software\Classes\htmlfile\shell\open\command) that needs addressing and automatically incorporates it for you.
Another thing that you may need to address is the Office 2003 service packs, make sure that your version of Outlook is service packed, patched and hotfixed to date.