pearPortVPN allows you to automatically establish a specific VPN connection whenever a wireless network of choice becomes available. Furthermore, it can automatically disconnect any open connections before your Mac falls asleep and thus safe you from annoying error messages about timed out connections when your Mac wakes up again.
Now you can also specify an IP-Range (IP-Address with the * character as placeholder, for example 10.1.1.*) to automatically establish a VPN connection when connected to the Ethernet port and the obtained IP-Address matches the specified range.
Mac OS X 10.5 PPC,
Mac OS X 10.6,
Mac OS X 10.5 Intel,
Mac OS X 10.6 Intel