not sure what you mean - openvpn has a client app for the n900, and also a GUI front end that lets you control the connection from the phone's status menu. You can download them from the repo's.

openvpn is also available for linux/windows, just download & install. It comes with sample conf files, how you tweak them depends on what you want to achieve - the ones in my first post are specific to my own requirements but would serve as a guide if you have a similar setup in mind.