The information you seek is here:
http://openvpn.net/index.php/open-source/documentation/howto.html#redirect
This describes how to setup openvpn so that all traffic is routed thru the vpn -- the redirect-gateway command creates a static route to your gateway, deletes your default route, then adds a new default gateway that routes thru the vpn. See also
The only steps you're missing from that is to add route to 192.168.x.x/etc which routes out your local interface. You can do this one of several ways, two of which are:
route network/IP [netmask] [gateway] [metric] (see the openvpn manual for more info) -- using this in openvpn config will have it set the routes for your rfc1918 addresses at vpn connect time
Using your os route command, add a static route to the routing table to tell it where to route rfc1918 addresses to. "route -p ADD 10.1.1.0 MASK 255.255.255.0 192.168.1.8". The -p command makes the static route persistent across reboots... if it's a non-windows OS, then setting the routes is done via several ways, and making it persistent across reboots is also done in several different distro-specific ways, so just check google for "create static route on " and you'll find the answer there.
Remember that more specific routing tables win over less specific, so adding a route for 192.168.x.x wins over a route to 0.0.0.0.