In your Program Files\Microsoft Visual Studio 2003\Common 7\VB7\VBProjects\ there is a file called "EmptyProject.vbproj"

This is an xml mile that defines your standard new project and it includes the imports section:
Code:
            <Imports>
                <Import Namespace = "Microsoft.VisualBasic" />
                <Import Namespace = "System" />
            </Imports>
Backup this file then delete the <Import Namespace = "Microsoft.VisualBasic" /> bit and then any new VB projects will not include the Microsoft.VisualBasic namespace.