Here is a way to set it up if you want to keep using the WRT160N for the wireless access but want to use your RV042 as your main router to be able to use VPN and better firewall capabilities:
1- Chane the Default Ip address of the WRT160N to something inside the RV042's network, (192.168.1.99 for instance)
2- Disable the DHCP server of the WRT160N.
3- Connect the RV042 to the internet, so it is the main router on your network
4- connect the WRT160N to one of the four LAN ports of the RV042.
With this setup, your RV042 will be the main router giving you access to the VPN capabilities, by disabling the DHCP server of the WRT160N you make all the devices on your network dependant of the RV042 while still able to use the wireless capabilities of the WRT160N as if it where a WAP.
This is just one of the many possible configurations.