Google if finally offering IMAP access for GMail
Finally, Gmail is supporting IMAP access.
You can read about it here: http://mail.google.com/mail/help/about_whatsnew.html
Here is the official help section on IMAP: http://mail.google.com/support/bin/topic.py?topic=1555
If you don't have IMAP option in your account's setting don't worry. It will show eventually.