A new version of the Transporter suite has been released that will aid you in moving from the systems above to Exchange 2007.
Download it from here
As an overview it does the following
Transporter Suite contains a set of tools for migrations from both Lotus Domino Servers, and generic IMAP/POP sources. For Lotus Domino the suite contains a set of tools for Directory and Free/Busy interoperability between Lotus Domino 6 or 7 and Exchange Server 2007 and Windows Server 2003 Active Directory. In addition for Lotus Domino the suite contains migration tools to migrate users, groups, personal address lists, mailboxes, personal mail archives, and applications from Lotus Domino 5, 6 or 7 to Active Directory, Exchange Server 2007, and Windows SharePoint Services 3.0. For generic POP/IMAP servers the suite contains a set of tools to bulk migrate mailboxes from any generic email servers that support the POP3 or IMAP4 protocol to mailboxes in Exchange Server 2007