If you configure your email correctly and make sure you have a valid email on your user in mp_Users, you can then use password recovery to get your password as it will decrypt it and send it to you.
Alternatively, if it is a new site and your user is the only user, if you manually change to clear text passwords by setting password format in mp_Sites to 0, then manually edit a new plain text password in the mp_Users, then recycle the app by touching Web.config you should be able to login and later you can change back to encrypted format.
Hope it helps,
Joe