The IT Stuff

ISA  Server 2004 SP3  includes the following new features or capabilities:

Improved Log Viewer
Enhanced Log Filtering
Improved Management of Log Filters
New Diagnostic Logging
Integration with ISA Firewall Best Practices Analyzer
Publishing Microsoft Exchange Server 2007 with ISA Server 2004.
With increased security
Enhanced troubleshooting tools
All software updates issued since ISA Server 2004 was released to manufacturing
Fixes for common issues reported by [...]

First of all create a new Access Rule.
Then select the  deny radio button, as we are not allowing these sites to be accessed.
Just choose the selected Protocols  and select the HTTP protocol under the Common protocols set or all outbound access.
Next step in the wizard is to specify from what sources these requests should be [...]

In ISA Server 2006 is that it is now possible to Publish SharePoint Sites with an ISA Server 2006 Wizard.
Through enhance wizard it is now also possible to Publish specific Exchange Mailserver versions. Exchange provides Publishing Wizards from Exchange 5.5 to Exchange V12.
ISA Server 2006 now also supports the Publishing of Load Balanced Web servers. Load [...]

It is useful to speedup internet access(Accelerator)  and to protect private network from public network(Firewall). It is actually firewall & acts as a proxy as well.
Types of firewalls:

Hardware firewall
Software firewall

Hardware firewall:

CISCO Pix
Watch Guard
Multi com Ethernet II

Software firewall:

ISA server
Checkpoint
Smooth wall

Firewall: A firewall protects networked computers from international hostile intrusions.