EXCHANGE SERVERS IN THE ORGANIZATION

Hi all,
I have a windows 2000 mased network at my office.
I have a server as “main domain -PDC”, another to store data and another 3th for the exchange 2000.
What i want to do is: have another exchange server to backup the main server, so in casethe “main” exchange server crash(get on fired) we will still have mail.
Is this posible? the new domain exchange server should be a child domain a new tree or a new forest?.
Also, if it is possible i will need to reformat the old exchange server (right now is very unestable), then i want to make sure that the “backup” server keeps all the information, mailbox, distribution lists, etc.

thanks all.