VPN Harware for Internet

I have had a client that has two offices in different towns. One has a SBS2000 Server installed with a router dialing in to the Internet via a ISP. The second office has one machine which dial into an ISP and create a vpn connection via Windows ISA Server. The second shop is now going to have four machines but they do not wont to buy a server.

What I wont to do is get to VPN cable routers which compress the data making the data transfer four times faster over the internet. I wont one at each end to make a perminst tunnel.

Has any one ever done this? Can some one give me tips? Have handy hints to give me. Maybe sujest a VPN Router (like Netopia)..

Help please……