Microsoft Internet Security and Acceleration (ISA) Server 2004 can implement a firewall, VPN, proxy and Web-cache server to help secure your IT resources.
Internet Security and Acceleration (ISA) Server 2004 is a combined advanced stateful packet and application-layer inspection firewall server, easy-to-implement virtual private network (VPN) server and Web proxy and cache server solution for your IT infrastructure
This combination of servers is only available through ISA Server, allowing you to maximize existing IT investments by improving network security and performance, all in one package.
ISA Server 2004 is available in two versions, ISA Server Standard Edition and ISA Server Enterprise Edition and is available in two forms:

• Hardware. You can acquire ISA Server 2004 Standard or Enterprise Editions on stand-alone hardware that comes shipped on a server with a hardened version of Microsoft Windows Server 2003 and a preconfigured version of ISA Server 2004. Deploy in under 15 minutes.
• Software. You can also acquire ISA Server 2004 Standard or Enterprise Edition as a software system ready for deployment onto your existing servers. Deploy, maintain, optimize, or even develop code on top of ISA Server to maximize the benefit.

With these options, you can mix-and-match to find the solution that works best for your company. As an example, you could buy and ship a hardware version of ISA Server to your branch offices and deploy the software version of ISA Server on multiple servers in your headquarters—it's up to you.