Does anyone know if you can override the default layout for the lookup page on an object?  I want to add a button to add a new record when needed.  For example, you start a new case on an account, and need to lookup the contact for the case.  The contact at the company has not yet been entered and is not in the lookup dialog.  I want to be able to click Add New to bring up the add new contact page to add it on the fly rather than having to go back and add the contact to the company before starting the case.  Any ideas?