Assuming these are networked together, basically, you would enter the IP address of the computer you want to connect to. It would be best if the computer had a fixed/static IP address.
For example, if you are using the MySQL Administrator program or Query Browser, you would enter the IP address as the "Server Host:" when you log in.
If you are using PHP, replace xxx.xxx.xxx.xxx in the following with the IP address of the computer you want to connect to -
PHP Code:
$link = mysql_connect('xxx.xxx.xxx.xxx', 'mysql_user', 'mysql_password')
or die('Could not connect: ' . mysql_error());