First off, you'll want to read through the openvpn how-to collection
http://openvpn.net/index.php/open-source/documentation/howto.html. If imagine that you're not running an insanely tight iptables configuration if you're new to the linux arena, so I'll go out on a limb and suggest that you need to add the following to your server configuration:
push "route 10.8.0.0 255.255.255.0"
If that doesn't solve your problem, please post your client and server configuration (sans comments).
-Stephen
