Connecting PHP 4 to MySQL 5

I recently upgraded one of our MySQL servers from 4.1.22 to 5.1.26. In the process of upgrading, I dumped all the databases, uninstalled MySQL then installed a clean copy of 5.1.26. Then I manually created all the users and schemas by hand, then restored our backups to the new install. Everything went smoothly and all the servers that had PHP 5.x installed could connect with no problems (because they used the latest version of the MySQL client API.)
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