Configuring a VPN behind ISA 2000

I have multiple servers running Exchange, SQL 7.0, ISA 2000, and a Primary as a Domain Controller. I want to set up a VPN for the whole Network, they are all running win2k advsrv. Do i need to configure all of these servers through RRAS of only the ISA server,or configure each on there own RRAS of each individual server?