Pro SQL Server 2005 Assemblies provides a detailed and example-driven tutorial on how to build and use .NET assemblies. The authors focus on building assemblies in C#, but also provide the equivalent VB .NET code in the supplied code download

Assemblies are not a complete replacement for T-SQL stored procedures and triggers; rather, they're enhancements, to be used at the right place and right time. This book examines the ins and outs of assemblies&emdash;when they should and should not be used, what you can do with them, and how you can get the most out of them