If you are using the build-in Cisco VPN Client in Mac OS X, you can also route your normal request beside the VPN tunnel. In the common OpenVPN client Tunnelblick, it's easy to setup these routes in the config file.
With the build-in Cisco VPN client, there is no preferences for these routes. The solution is to add these missing routes via Terminal.
Your local network has IPs like 192.168.1.X
sudo route -nv add -net 10 -interface utun0
This line routes all IPs starting with 10 through the VPN tunnel. 10 is here the net on the other side.
sudo route change default 192.168.1.1
This line route all other requests through through your local gateway (router). In my local network my gateway has the IP 192.168.1.1 an I have an 192.168.X.X local network.