Best placement of a VPN and Firewall

I am redesigning a small Windows 2000 network with approx. 60 users, multiple servers, a PIX firewall and a Cisco VPN 3000 concentrator. The site currently has a T-1 with a Cisco router. I’m wondering about the placement of the VPN and firewall. I will be running both a web and exchange server. Should I put the VPN and PIX behind the router, in front, or parallel? Any thoughts?