Two <img src=/S/free.gif border=0 alt=free width=30 height=15> programs I hadn't come across before:

Genie-Soft - FREE Outlook Express Backup
MailStore - Email Archive and Backup for Outlook PST, Exchange and IMAP

MailStore Home archives email from:
Microsoft Outlook 2000, XP, 2003 and 2007
Microsoft Outlook Express and Windows Mail
Microsoft Exchange Server Mailboxes
Mozilla Thunderbird and SeaMonkey
POP3 and IMAP (including webmail services such as Gmail and Yahoo)
.eml and other files

Genie-soft is for OE only. Both appear to be very capable, with useful feature sets.