Starting with Visual Basic 4.0, you can add conditional compilation statements and use them to create different versions for 16-bit and 32-bit environments or to call debugging DLLs while testing your applications. However, you have to be careful when you use the setup wizard to generate the installation package because those files will be included unless you remove them from the distribution list. It is even worse when 16-bit code is upgraded to VB5 because some of the 16-bit DLLs are no longer included in the operating system, such as USER.DLL. In this case, you have to comment out all the references to these libraries.