Setting Profile with Group Policy

We aer a medical facility and have a generic user profile for visiting and rotating physicians. All permanent employess have their own username and password. We can track where they go regarding internet use. The problem is some folks are using this generic profile (pushed) to browse to inappropriate sites. We try to black all that we can but some folks still find a way. We want this generic profile to be able to browse to our intranet but not the internet. Have otehr folks run into similar situations? IF so how did you handle this. Did you use Group Policy? Any ideas on how best to implement this?
Any help is greatly appreciated.
Sincerely
Marc Larouche