Mr. Cisco with one biased solution!
Here is a hardware solution providing that everyone has broadband in their homes, and you have a static IP where the "server" is:
12 X Cisco 3002's
1 X PIX 506 (25 VPN's max)
Probably more expense in initial cost than some other options (when is Cisco the cheapest option?) but rock solid, and support from Cisco TAC is pretty cheap on these devices.
I would rather not have my feet held to the fire when a crazy custom solution fails and 12 people can't work! I always figure that into the total cost of a solution.
Whatever you go with, good luck!
Unsolved 
