You can set an ipsec filtering policy on the "computer" to manage what
outbound ports that users on a computer can access, block access at the
firewall with the computers IP address [static would be best], or configure
the computer to not have a default gateway to prevent any access outside of
the network for that computer. A user based solution [other that ISA as
Phillip mentioned] could be a personal firewall such as Portslock that can
have different configuration based on logged on user or using Group Policy
to configure a "bogus" proxy server for that user being sure he could not
access IE settings to reconfigure which would prevent internet access only
through Internet Explorer.. --- Steve