If I were you, I'd concentrate on the VPN part of the problem and ignore the wireless. Modern OSes support wireless easily enough that you can make it work like ether and forget it.
If all your PCs (including the firewall) are running Linux, I'd use CIPE for the VPN. If you need interop between platforms, or you need other platforms, I'd probably go with IPSec, although the CIPE for Windows project might be worth taking a look. If your firewall box has at least 16MB of memory, and a few hundred MB of hard disk, you oughta be able to do the job with Linux. Maybe even less hardware with one of the custom appliance distribs of Linux. -Bennett
