I had to modify the htmlfile registry key to get HTM and HTML files to open in TextPad using the EDIT context menu for the file types, and in IE 6 itself, using the "known issues" suggestion from the help system. The -s parameter has to be changed to "%1" and the DDE key removed. So the key looks like this
Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT\htmlfile\shell\edit]
[HKEY_CLASSES_ROOT\htmlfile\shell\edit\Command]
@="\"C:\\Program Files\\TextPad 5\\TextPad.exe\" \"%1\""
Internet Explorer -- Problem with Edit menu under Textpad 5
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