Error accessing MySQL server from PHP

I've installed MySQL and I find I can use it from the 'mysql' command,
however when trying to use it from a PHP script I get this:

Warning: mysql_connect() [function.mysql-connect]: Lost connection to
MySQL server at 'reading initial communication packet', system error:
111

Anybody know what this signifies and how to fix it? My set up is very
simple.

Thanks.