It's quite simple really. The role you need to install is called Network Policy & Access Services
- When the Wizard asks you which services you want to install, choose "Remote Access Service" and "Routing". Once that role has installed, right click on it's name in the Server Manager winow, and press "Configure and Enable routing and remote access".
Choose custom configuration in the wizard, then pick "VPN Access" and "NAT". Then, press "Finish". When it asks you if you want to start the service, press yes.
Then, go back to the Server Manager window, and right click on "Routing and Remote Access". Then, choose Properties, and go to the IPv4. Then, click the radio button next to "Static Address Pool", and press Add. Choose the range of IP addresses you want you computers to have (I normally choose 192.168.1.1->192.168.0.254), and press OK.
Now, the VPN Server is configured! All you need to do now is let users connect.
I'm assuming that you are not using Active Directory...
Open up the "Computer Management" window, and choose the "Local users & Groups" option on the right. Click on the Users Folder, then Right click on the user who you want to have VPN access, and press "Properties". In the properties window, click on "Dial-in", then press the "Allow Access" in the Network Access permissions section.
That SHOULD work.... But it's not TOTALLY tested! Any Problems, let me know