Why do you have to use Outlook? If you could use CDO for Windows 2000 and latrer, this is a piece of cake. You can even set the sender;s e-mail address to be Daffy@duck.com if you want to. And CDO does not rely on the e-mail client installed on the local machine. All you need is access to an SMTP server.
Because that is what my client wants. :-) I recommended that we move to another mechanism for sending the mail for many reasons. The show stopper was that Outlook provides the end user with an audit trail in the same location as the rest of her email. They don't want to have mail information for one purpose stored in one place and manual company email in another. Shortly they will be implementing exchange server and they want this mail to eventually go through the exchange server too. I think the best answer will be to wait until they finish implementing the upgrade to Outlook 2007.