I have a cisco VPN on my main (work) laptop on my home network connected to a BTHub3 wireless router. When the VPN is connected other devices (laptop or IPhone)frequently have to be re-connected to the network to browse the internet

At a guess it would sound like the vpn is causing your modem to "hang" and drop the other devices. You can check to see (with google) if that is a common problem with your router, if so then sometimes updating the firmware can fix the issue. Otherwise you may need to look into getting a different router.

Still more information would be best. Do devices ever fall off your network under heavy load(such as streaming high def movies)? Your vpn probably needs custom access/ports to be set on your router are they? Is anyone else at your work experiencing this problem with the vpn going through their wireless setup?