From Techtarget
"Site-to-site VPNs connect entire networks to each other -- for example, connecting a branch office network to a company headquarters network. In a site-to-site VPN, hosts do not have VPN client software; they send and receive normal TCP/IP traffic through a VPN gateway. The VPN gateway is responsible for encapsulating and encrypting outbound traffic, sending it through a VPN tunnel over the Internet, to a peer VPN gateway at the target site. Upon receipt, the peer VPN gateway strips the headers, decrypts the content, and relays the packet towards the target host inside its private network."
Routing and Remote Access in Server 2003 can be used but then you would have to let one sever at each site have one NIC connected directly to the Internet (public IP).
