You use one router for your VPN and the other for general Internet
activities, so what you’ll need to do is create multiple route entries
in your Windows machine, so it knows when it should use either router.
The easiest way to achieve this would be to set as a gateway the router
you use for your main Internet connection, and then use the following
commands to pass all traffic related to your VPN through the VPN router:
'route –p add <vpn network> mask 255.255.255.0 <vpn router IP>'
You’ll need to repeat this commands depending on the number of networks you need to contact through your VPN.
option makes the route entry permanent, meaning
that if you reboot your PC, these entries will still remain in your
routing table so you don’t need to retype them.
refers to the VPN network you need to access, (e.g.,
192.168.70.0), and the mask parameter is standard, assuming your
networks are Class C type.
In closing, the <vpn router
IP> is the IP address of your VPN router. I think that pretty much
covers it. Remember that you’ll need to create multiple entries for each
VPN network you require to access!