take a look at this site:
http://maemo.org/maemowiki/InstallVPNC

or if you want to use openvpn:
http://www.rahkonen.org/openvpn.html

its also my opinion, that the nokia 770 is a great little device. its amazing what you can do with it.
here is also a link to the howto summary of maemo:
http://maemo.org/maemowiki/HowTo

have fun with your device