LINUX to Exchange migration.

Hi.
My client wants to migrate from his LINUX Email and Web Server to Exchange 2000 and ISA Server Firewall/Proxy. I have done BOTH parts, ISA and Exchange, but still did NOT public the Exchange through ISA for administrative reasons.

Both Linux and Exchange are on the same LAN. My question is:
How can I IMPORT MAILBOXES and USERS from the LINIX server directly into the Exchange Server?
Importing users is not of that importance as much as importing messages and mailboxes!
N.B.
1: The Linux server is going to be removed from the LAN.
2: I prefer not to alter the LINUX server
3: Prefer to have detailed answer, maybe utilities and commands to use.
4: Please contact i.abedrabbo@intersistemi.it

Thanks