Microsoft Internet Security and Acceleration (ISA) Server 2004 is the advanced application layer firewall, VPN, and Web cache solution that enables customers to easily maximize existing IT investments by improving network security and performance. ISA Server 2004 Beta allows you to preview the upcoming functionality in this upcoming version.
http://www.microsoft.com/isaserver/beta/default.asp
http://www.microsoft.com/isaserver/beta/default.asp