Hi Dan,
In ArcGIS 9, you can put your vba code and button in the Normal template, which makes it global. But that is no longer supported starting at ArcGIS 10. So if you're using 10, you need to create an Add-In. You indicate you're using the Express edition of Visual Studio, so you will have to use VS 2008, since that's what the SDK installer supports. You should be able to simply reinstall the SDK to get the ArcGIS templates into VS.