Sure, you can use group policy to restrict the internet access. these how to
may help.
how to restrict internet access
     How to restrict Internet Access. You may have many options to disable
a user or computer to access the Internet. Some options can be adopted for
many users ...
     www.howtonetworking.com/Internet/restrictie0.htm  - Similar pages

Setup Group Policy to restrict internet access
     This article descript how to use Group Policy to restrict Internet
Access by assigning a fake IP to proxy. In our case, you have some clients
accessing your ...
     www.howtonetworking.com/Internet/restrictie11.htm