How to back up gmail to my computer?

There are many ways to do this:

• Matt Cutts: How to back up your Gmail on Linux in four easy steps
• Back up Gmail with fetchmail
• Backing up Gmail with Thunderbird
• Gmail Backup utility
• BackupMyMail

Most email clients when viewing over IMAP will clearly distinguish between the IMAP store and the local store.

Simply copy the messages / folders to the local storage using your email client's copy command, and it should copy the messages in the local storage.

Make sure not to move them, since this will more than likely remove them from the email server.

Edit Outlook seems to handle IMAP servers a lot better than Thunderbird does from my experience. Perhaps it would be a good idea to get a copy of Office 2003 / 2007, and work from that? (Legal copy of course :P)

All the major windows clients (Thunderbird, Outlook) will clearly differentiate between the local storage and the IMAP store. Not sure about Windows Mail or OE though.

http://www.gmail-backup.com/