In general, an AutoCAD 2007 automation project created in the VBA IDE or created with Visual Basic 6 should work with AutoCAD 2008.
AutoCAD 2008 automation projects use the type library acax17enu.tlb. The type library is located in the following folder: C:\Program Files\Common Files\Autodesk Shared.
AutoCAD 2008 automation projects use a different version-dependent ProgID than AutoCAD 2007 for the CreateObject, GetObject, and GetInterfaceObject methods. For example, if you are using the CreateObject function in an AutoCAD 2008 automation project, you use CreateObject ("AutoCAD.Application.17"). If an automation project uses version-independent ProgIDs, change the project to use version-dependent ProgIDs.