Don't worry! It's only stuff...

extract p12 file
Zertifikat des Benutzers:
openssl pkcs12 -in *.p12 -clcerts -nokeys -nodes -out user.pem

Zertifikat der Zertifizierungsstelle:
openssl pkcs12 -in *.p12 -cacerts -nodes -out ca.pem

Privater Schlüssel:
openssl pkcs12 -in *.p12 -nocerts -nodes -out keys.pem

config file
tls-client
client
dev tun
proto udp
tun-mtu 1400
remote YOUR_HOST.dyndns.org 1194
ca ca.pem
cert user.pem
key keys.pem
cipher BF-CBC
comp-lzo
verb 3
ns-cert-type server
tls-remote YOUR_HOST.dyndns.org
float

Connect to Client in same IP range
route add 192.168.1.31 dev tap0

OpenVPN Gui (Client for Windows)
http://man.chinaunix.net/linux/efw-admin-guide-html-chunk/efw.vpn.openvpn.html

C:\Programme\OpenVPN\config\YOUR_VPN.ovpn (old)
client
proto udp
remote YOUR_SERVER.dyndns.org
resolv-retry infinite
nobind
persist-key
persist-tun
ca YOUR_CERT.cer
auth-user-pass
comp-lzo
dev tap

Configure Gnome Network Applet for Endian
VPN-Connections > VPN-Configure
Add
Create
Connection Name: YOUR_VPN_NAME
Gateway: YOUR_VPN_SERVER_IP
Type: Password
Username: YOUR_VPN_USER_NAME
Password: YOUR_VPN_PASS
CA Certificate: YOUR_ENDIAN .pem file

Advanced:
Use LZO Data Compression: checked
Use a TAP Device: check
OK

IPv4 settings > Routing:
Add
Address: YOUR_VPN_NETWORK (192.168.1.0)
Netmask: 255.255.255.0

Links
http://www.ipcop-forum.de/forum/viewtopic.php?p=167998
http://www.ngs.ac.uk/useful-openssl-commands
http://www.sven-kuegler.de/tag/openvpn
http://www.ngs.ac.uk/useful-openssl-commands
http://man.chinaunix.net/linux/efw-admin-guide-html-chunk/efw.vpn.openvpn.html