Regaining access to Joomla 3.2 when downgrading php below 5.3.7
From Joomla! Documentation
When a Joomla 3.2 site is created on server using PHP v5.3.7+, and then moved to a server with a version of PHP less than 5.3.7, access my break to changes in password hashing by the version of PHP. There are a few techniques for regaining access.
NOTE Downgrading PHP to a version less then 5.3.7 is not advised due to bugs in those versions of PHP's password hashing.