Hi,
Which mail application are you using?
If you using Outlook Express or Entourage 2001 then all your mails will be
stored under <Harddisk> / Documents / Microsoft User Data.
Copy the Microsoft User Data folder and move to the same location on the new
computer.
If you are using Entourage X or Entourage 2004 the mails address book,
calendar etc will be stored under <Hard Disk> / Users / user's folder ( Home
folder) / Documents / Microsoft User Data. ( If you are using Entourage X
the Entourage data will be stored under Entourage X identities & if you are
using Entourage the its data will be stored under Entourage 2004 identities
under Microsoft User Data folder.
I would suggest you to copy complete Microsoft User Data folder and move to
the same location on the new computer.