check into "OpenDoc"
You should use ISldWorks::OpenDoc6, like in this example. You can see where you'll need to replace the path I've provided with the correct path.
Dim swApp As SldWorks.SldWorks Dim strPath as String Sub main() Set swApp = Application.SldWorks strPath = "C:\myDrw.SLDDRW" swApp.OpenDoc6 strPath, swDocDRAWING, Empty, Empty, Empty, Empty End Sub
You could also record yourself opening a part and then use that code. I explain how to use the macro recorder in lesson 2.1 in the Videos section of my web site.