I need help setting up a VPN

At my office they are trying to setup a VPN from the offices in Chicago to the offices in New York. No tech help is coming from the ISP or the offices in New York, and I am the only guy who can come close to making this happen unfortunately.

For the hardware we have a Linksys Cable/DSL router and a VPN Cisco Pix 501 firewall. How do I go about configuring the hardware on the network? My first inclination is to setup the pix on the DSL line and then setup the router on the inside of the network, but I really have no idea. What is it that I have to be careful of when I am doing this?

I am afraid I am in over my head, but it would be great if I could make this happen, any help would be appreciated.