What is the best way to force users to use a VPN?

The company is a small (50 stations) business with a number of the stations off site and we use a VPN to connect the computers to our network to update clients. How can we 'force' the users to log into the VPN as data for the clients is health related and needs to be secure. We use Microsoft's small business server.|||By only allowing access to the server through the VPN and blocking all other access.|||take a look at the business and technical forums at www.montagemarketing.co.uk I hope this helps. If not pm I maybe able to do something for you