I found that newest php works with its own mysql (5.0.9, or so) and it's not using mine. I'd rather install back the one shipped with Leopard if I had to go versions back.
Also, I couldn't get it to work (#2002 error, sockets were there but still not working) and once I uninstalled it, it was supposed to leave the OS untouched, but Leopard's didn't come back to life. I had to add the following lines to httpd.conf, otherwise the php code was shown, instead of executed.
AddType application/x-httpd-php .php .phtml
DirectoryIndex index.html index.php
I'd think I saw the previous mysql folders somewhere and Leopard making an alias to the right one somewhere. Do you remember where?