What’s best for migrating to EXchange 2k3

Dear All,
I recently decided to change our mail system from my present mail server to Exchange 2003.

The old system involved a Domain POP account which POPed mails from a catchall for distribution to different accounts. You may all scream why DPOP ? Simple my mails are hosted somewhere else which allows for a fail-over in the event of a downtime at my site or a malfunction on the server (as it has occured recently ) Business continuity still goes on both for local staff and remote employees

Could you all suggest how to set same config if I move to Exchange, or at best recommend a best solution with business continuity in mind. No hosting solutions pls.

Thanks