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. In ISA Server 2004 we have redesigned its user interface by replacing the standard Microsoft Management Console (MMC) plug-in used in the first version.
In addition, we have also made significant architectural updates based on customer feedback. The following is a quick comparison of the major architectural differences between the two versions of ISA Server. More informations and download here