OpenVPN project has its own website, including downloads of new versions and updates, documentation, howtos, mailing lists, and links to various VPN-related pages. A project page can hardly be better than that of OpenVPN. You'll find it at http://openvpn.net/.
The most important source of help is the mailing lists: http://openvpn.net/mail.html.
Since we are using SSL/TLS for encryption purposes, you certainly want to understand this toolkit. The SSL/TLS Cryptographic libraries website provides detailed documentation and mailing lists, which can be found at http://www.openssl.org/.
The website of the TLS Charter by the TLS Working Group provides a list with many related RFCs and Internet drafts you might consider helpful: http://www.ietf.org/html.charters/tls-charter.html.
The Universal TUN/TAP driver can be downloaded from the following page: http://vtun.sourceforge.net/tun/. Nevertheless, this should not be necessary, since every modern distribution (and kernel) should...