No, and thats the whole idea. If you store the MD5 hash of a password you should not be able to determine the original string that generated that hash. Using the MD5 hash AS a plain password makes the system even less secure.
Note: MD5 is known to be cryptographcially weak, and it is now possible with a reasonable ammont of effort to generate a string (not neciccarly the original string) that results in the same MD5. This method is not reasonable for a php login script, however.