Mac OS X (10.4) – Dial-up Config

To open System Preferences choose the icon from the Dock.

Under ‘Internet & Network’ choose ‘Network’.
This will then show the available methods of connection.

Choose the item you want to configure and click the ‘Configure...’ button. The following page then shows the IP Address and Router and allows you to input your own DNS Servers. For fixed IP under ‘Configure IPv4’ choose ‘Using DHCP with manual address’ then simply enter the IP Address you want.