Microsoft Knowledge Base Article 303817 contains the following summary:

This article describes how to set up Transmission Control Protocol/Internet Protocol (TCP/IP) for Network Load Balancing, which is typically the last step of a Network Load Balancing installation.

Network Load Balancing enables you to spread incoming requests across as many as 32 servers. This feature enables you to expand enterprise-wide services, such as, Web servers, Terminal Services, and streaming media servers, and still ensure that they can respond quickly, even under heavy loads.

Network Load Balancing automatically detects the failure of a server and quickly reassigns client computer traffic among the remaining servers. This safeguard can help you to provide uninterrupted, continuous service for your critical business programs.