Disable Internet for a group of PCs
At the moment I seem to be asked this question every month! Here's how I do it using Windows Server 2003 Group Policies!
Wherever your workstations are located in your domain structure, create another sub OU, so for example:
Root - Curriculum
Sub - Pupils
Sub - ICT Suite
Sub - Classrooms
Sub - Block Internet
Create another sub OU called Block Internet. Within this OU create a new GPO. Call that Block Internet too.
Now navigate to: Computer Config > Windows Settings > Security Settings > Software Restriction Policies.
For the first time, right click Software Restriction Policies and choose New Software Restriction Policies. Double click Additional Rules. Right click in an empty space and choose New Path Rule
Enter the path: C:\Program Files\Internet Explorer\iexplore.exe, choose Disallow from the drop down menu and in the description put Block IE.
Now move the relevant Computer objects into this OU. The workstations will either need to be restarted a few times, or use gpupdate /force from the Run menu and then restart.
This should block every attempt at connecting to the web by any user and doesn't require any scripts or third party utilities.
I hope you find this useful. Maybe you do things differently? Care to share? :)