Can creating a useful and secure VPN be as simple as employing Linksys BEFVP41 VPN routers in two or more LANs to be connected together via the Internet? It seems almost too good (and too cheap) to be true.
Technically you could create a VPN using two low-cost boxes and by that I mean establish a VPN tunnel. But practically, you may find that the packet processing and encryption processing consumes so much power that the net throughput is just a trickle. Also, it's likely that the method of authentication will be simple shared secrets -- these are easily hacked. So for a truly secure, high performance VPN, you'll need a little more.
However, depending on your security needs these boxes may be fine. Remember that VPN is not only a security technology, but also a networking technology that can map to LANs together even if the traffic is not encrypted. If your goal is simple communications and security isn't that important, you might try running the Linksys boxes with NULL encryption (encryption turned off). This might give you the performance you need and provide an inexpensive way to bridge to LANs.