You're not going to offend me, I don't have a dog in that fight. But I don't understand why, after given a proper response, you'd continue on trying to justify doing the wrong thing.
The proper response for you and your boss is migrate the domain AD to contain at a minimum 2003 DC's, no 2000 DC's anywhere near the domain that your Exchange server is in. 2000 member servers are fine. Once you have completed that task, *then* bring up a new Exchange 2007 server into the environment, migrate your users over to it (making sure they have at least Outlook 2003 to avoid other issues), and you're all set.
If you don't want to do that, and instead wish to see what happens when you bring a 2007 Server up into an environment that contains a 2000 DC and then "fix" what problems occur after that, you go right ahead. You won't offend me, I promise.
I'm Certifiable, not cert-ified.
It just means my answers are from experience, not a book.
There are no more PDC's! There are DC's with FSMO roles!