1) Yes, you can use CommandBars techniques to hide/show any toolbar or
individual command, except the menu.
2) Plaxo is not customizing a message form; the consensus seems to be that
they're using low-level Windows programming to overlay a button on the
Outlook item window.
You didn't say anything about the scope of your application and it would
actually be doing. That would have a bearing on the approach.

Signature
Sue Mosher, Outlook MVP
Author of
Microsoft Outlook Programming - Jumpstart for
Administrators, Power Users, and Developers
http://www.outlookcode.com/jumpstart.aspx
> Hi,
>
[quoted text clipped - 10 lines]
> Regards
> Nauman