Probably the easiest would be to keep the wireless communications open, and use a VPN concentrator running to an SSL VPN client on the laptops/pcs.
All they'd have to do is aim their browser that the VPN gateway, and allow the SSL client to be downstreamed to their computer.
Beyond that, use your BBSM proxy or provide user auth at the VPN concentrator.
Leave the SSID in broadcast mode ("guest").
With this system, most clients can find the wireless system (SSID broadcast), the encryption via the SSL VPN is very strong, and there'd be no real configuration for the clients. Just aim the browesr at the VPN gateway/concentrator and enter the username and password.
Also, make sure you enable "Public Secure Packet Forwarding" (PSPF) to prevent one client from attacking other clients on te wireless LAN.
Users that use the system on a regular basis could get / use certificates for authentication. If they're on the system a lot, then the minor grief of setup would be worth it.
The SSL client uses Java, I believe, so it should be fairly universal (i.e., not platform specific). I haven't tried te SSL client n any system other than MS Windows so I can't really comment on *nix or Mac.
The SSL gate ( 3000 series) that we use for our Lab access seems to work pretty well.
Good Luck
Scott