How to route several devices in my network through a hardware VPN device, by changing the gateway?

view story

http://superuser.com – I have a network at home with a 60Mbit cable connection to the internet via a modem I can't access (supplied and maintained by my Internet provider). Behind the modem I have a netgear WNDR3700 wireless router, that has enough throughput for my connection. Behind the netgear there are a couple of switches in different locations around the house with different devices attached. I have recenty purchased a Netgear FVS318G Firewall with VPN, so I can tunnel to a VPN network. The thing is this FVS318G only has 25Mbit LAN/WAN throughput, and 7Mbit VPN throughput, so I don't want to use it for every (HowTos)