Exchange Mailboxes

We have a single exchange server at our site. We are doing an entire network rebuild, and want to use new hardware for everything. Our existing exchange server is in deperate need of attrention, and we do not want to restore the entire server from backup. We would prefer to back the individual mailboxes up, and restore them on a new server, as our entire information store seems to be corrupt. How would we go about foing this ? ( we have Backup Exec v7 ) This is an urgent matter, and any help would be most appreciated !! Many Thanks.