by using your original license copy of outlook (Office Suite) CD, without uninstalling (from add/remove), re-install it, and it will get fixed.
TWB - Also within, at least Outlook 2003, in the main 'Help Tab', there is a "Detect & Repair" link that will also fix most problems. Within it though, there are two additional check boxes, one is to "Restore my shortcuts while repairing", the other is "Discard my customized settings and restore default settings". Normally, the 1st one, only, will repair most problems. If the problem continues, use both buttons, the 2nd one is more destructive, so you will lose all of your customization as far as WYSIWYG, not your email signatures or other things like that. It will also complain, until you close Outlook, that it and maybe Word, if you use it for your email editor, are open and running. Go ahead and close Outlook, the fix will still continue to work. It will require your attention within the 1st minute or two, stating that it has completed restoring the defaults, press OK, and then you can walk away for a few minutes without further intervention.