How do I create a menu shortcut which involves the delete key?
You can edit the property list that stores the shortcuts directly. For example open ~/Library/Preferences/com.apple.AddressBook.plist with TextMate or TextWrangler, and add:
<key>NSUserKeyEquivalents</key>
<dict>
<key>Delete Card</key>
<string>~@</string>
</dict>
The shortcut strings are documented in http://www.hcs.harvard.edu/~jrus/Site/Cocoa%20Text%20System.html.