There are many examples how to setup a Virtual Private Network (VPN) connection for your Mac but most, if not all, are pre-Leopard using the Internet Connect application, which is no longer part of Leopard. 

Here are the instructions for Leopard (OS X 10.5.x). You must have Admin privileges to make the changes.

For this example, we will use “vpn.illumonus.com” for the server address, “ANTIOCH” for the domain and “Klaus Naujok” as the user account name.

We start by selecting from the Apple menu the System Preferences option:

Within the System Preferences window we click on the Network icon:

If the lock (blue box) is closed you need to click on the lock and enter the admin password to open the lock to add the VPN service. Now click on the + button above the open lock to start entering a new interface service:

From the Interface pop-up menu select the VPN for the Interface, PPTP (you may have to select L2TP over IPSec, check with your Administrator) for theVPN Type and enter Home Office for the Service name. To continue click on the Create button:

The Network pane will now show the blank VPN setup window:

Enter the Server Address (vpn.illumonus.com) and the Account Name, using the “domain/FirstName LastName” format, (ANTIOCH\Klaus Naujok). Also select the “Show VPN status in menu bar” option which will allow you to easy connect and disconnect. When done we will click on theAuthentication Settings button to continue:

 Enter the user authentication information (your password) and click on the OK button:

We are almost done. To continue click on the Advanced button:

In the new window make sure the Options pane is selected, if not select it by clicking on it. Select the “Send all traffic over VPN connection” by clicking on the square. Leave the rest as they are. Now click on the DNS button to go to the next pane:

In the DNS pane add the default DNS server IP by clicking on the + button, in this case 192.168.1.100 (check with your IT department if you don’t know the IP address). Also add any domain to search, in this case enter antioch.local by clicking on the + button on the bottom of the Search Domains entry field. When done click on the OK button.

We are back at the Network window. Since we entered all information, we will click on the Apply button to save the changes.

To prevent further changes we will click on the lock icon to close it.

The final step is to close the System Preferences by clicking on the red bubble (top left hand side of the Network window).

To use the new VPN service to connect as well as disconnect checkout the VPN Usage page by clicking on this link.