To use ISA Server, you need:

• A personal computer with a 550-megahertz (MHz) or faster processor.
  
  
• Microsoft Windows Server™ 2003 operating system with Service Pack 1 (SP1) or Microsoft Windows Server 2003 R2 operating system.
  
  Note the following:
  
  
  • You can not install ISA Server 2006 on 64-bit versions of Windows Server 2003 operating systems.
    
    
  • When ISA Server 2006 is installed as a domain member, ISA Server Standard Edition can be installed only in a Windows Server 2003 or Windows Server 2000 domain.
    
    
• 256 megabytes (MB) of memory.
  
  
• 150 MB of available hard disk space. This is exclusive of hard disk space you want to use for caching.
  
  
• One network adapter that is compatible with the computer's operating system, for communication with the Internal network.
  
  
• An additional network adapter for each network connected to the ISA Server computer.
  
  
• One local hard disk partition that is formatted with the NTFS file system.
  
  

  Note:

  You can use ISA Server on a computer that has only one network adapter. Typically, you will do so when another firewall is located on the edge of the network, connecting your corporate resources to the Internet. In this single adapter scenario, ISA Server typically functions to provide an additional layer of application filtering protection to published servers, or to cache content from the Internet. For more information, see "Configuring ISA Server on a Computer with a Single Network Adapter" at the Microsoft TechNet Web site.

  Caution:
  Do not install ISA Server 2006 Standard Edition on a multi-processor computer with more than four processors.