I have passwords for members on a site encrypted using MD5 and stored in the database. I want to implement a lost password functionality where the user will be emailed their
You can't recover the original password from the MD5 hash. It's a one way hash function.
You shouldn't be providing them with the plain text password. What you should do instead is either allow them to change the password, or generate a random one for them to use and then force them to change it.