Split domain setup questions

[TerranAce007]

Hey guys,

I am the IT guy for a small company with about 100 users. We recently upgraded our single server from SBS 2003 to Server 2003 w/ Exchange 2003 and a new file storage server. Right now, we only have the one domain controller and the NAS server. Our users use Outlook 2003 in the office and Outlook Web Access remotely.

I am planning to setup a third system as a backup Server 2003 domain controller. Having a exchange backup would be a big plus, but if I could use Zimbra instead, it would save a lot of money on exchange software & licenses.

I read the how-to on configuring Zimbra in a split domain, but I'm not sure if thats really what I need. I would like the Zimbra server to host all the same users as exchange and keep all their e-mails/contacts/calendars so that if our primary server goes down, our users could just open up the Zimbra webmail and use it until we get our exchange server back online. Once back online, I would need all the e-mails received through Zimbra to also be forwarded to the exchange server so users don't complain about missing e-mail when they go back to outlook.

Is a setup like this possible and easily configurable?

Thanks!