Microsoft finally made this a part of Exchange

Exchange 2007 finally has the ability to add a custom footer or a disclaimer on all outgoing e-mails as a native part of Exchange. No more fumbling around with odd VBScripts, registry hacks, and third party tools. The Daniel Petri site at http://www.petri.co.il/transport-rules-adding-a-disclaimer.htm has a good explanation. I like the warnings at the bottom about that are basically "this will affect everyone, test it first"...