Microsoft Visual Basic for Applications (VBA) is the programming environment and language for Microsoft Office that has been available for several years. Microsoft Office 2003 Editions have a new environment for building applications, called Visual Studio Tools for Office, which is based on the Microsoft .NET Framework.
Microsoft Visual Studio Tools for Office, Version 2003, offered many advantages over VBA, but Microsoft Visual Studio 2005 Tools for Office enhances these features for even more user productivity.
This article analyzes many solution migration issues that you may face when using the Visual Basic language to directly migrate a VBA solution to Visual Studio 2005 Tools for Office. The
Source : Migrating Excel VBA Solutions to Visual Studio 2005 Tools for Office