Visual Basic 6.0 Compatibility Library
If you have used previous versions of Visual Basic, you will notice that Visual Basic 2008 introduces several changes to the Visual Basic language and that some familiar functions have seemingly disappeared. These changes were necessary in order to make Visual Basic compliant with the .NET Framework and the Common Language Specification (CLS).
When a Visual Basic 6.0 application is upgraded to Visual Basic 2008, the conversion of some code is impossible, due to syntactical or architectural differences. For this reason, functions in the Visual Basic 6.0 Compatibility library (Microsoft.VisualBasic.Compatibility) are used to allow the code to run in Visual Basic 2008 without the need for extensive modification. These functions mimic Visual Basic 6.0 behavior, while remaining compliant with the Common Language Specification. Wherever possible, the upgrade tool attempts to move your code directly to functions in the Microsoft.VisualBasic or System namespace.
Although the functions and objects in the Compatibility namespace were designed to support the upgrade tool, there is nothing to prevent you from using them when creating a new application in Visual Basic 2008. In most cases, however, the .NET Framework provides richer functionality.