If you are trying to get PHP, Apache and MySQL to work together one of the steps you have to do is edit the file /etc/php5/apache2/php.ini and uncomment the following line,
extensions = mysql.so
You then need to commented out the following lines,
;extension_dir = /usr/lib/php4/20020429-zts/
;include_path = ".:/usr/share/php"
NOTE : These are the only steps of course, its just one of the traps I came across while trying setup a server.