If you are interested in clustering SQL server, then the following links provide a great place to get started:

SQL 2000

SQL Server 2000 Failover Clustering

SQL Server 2000 High Availability Series

FAQs - SQL Server 2000 - failover clustering

SQL Server 2000 Clustering Tips

How to Install SQL Server 2000 Clustering

Support WebCast: Microsoft SQL Server 2000 Failover Clustering Disaster Recovery Procedures

SQL 2005

SQL Server 2005 Failover Clustering White Paper

With thanks to my colleague Gareth Ford for these.