How to know which DLL file to use when executing a file written in a particular version of Visual Basic in different Windows operating systems:
The difference between the Win6400.DLL and the Win95600.DLL file is that the Win6400.DLL operates in a 16 bit format, where the Win95600.DLL operates under a 32 bit format. Therefore, if you wish to use a program that is written in VisualBasic 3.0 (a 16 bit system), then use the Win6400.DLL file. However, if you wish to use the Win956000.DLL file, you must upgrade to and write programs using VisualBasic 4.0 or newer (which are 32 bit programs). This procedure is valid whether you are using Windows 3.1, Windows 95 or Windows 98 operating systems. Users of Windows NT must use the NT6400.DLL file.