Registry, customize "Save as Type" for Word + Excel

Two questions:
1. How can I customize "Save as type" list for Word and Excel.
I have modified the Save/Open file-filters for non application programs like Paint and a script editor "Metapad".
In fact Metapad installation taught me a lot about the Registry, but just enough to be very cautious and dangerous.
Do I have to add more sub-keys to existing keys?
Metapad introduced a Registry Entry "FileFilter" but a search does not turn up any other "FileFilter" entry.

2. When customizing file associations in WinExp | Tools | Folder Options | File Types ... Windows dumps "Open" and "Edit" on the WinExp right-click list, even though neither "Open" nor "Edit" are one of the "Actions"
How can I ensure the file > shortcut menu does not inherit MS over-kill.

Trawling google is proving to be a no win.
XP sp2
Office 2003
Thank you to anyone who can help.