Try adding the Dll file to your project and use intuition to decalare some instances of the possible classnames inside. If the vendor has no documentation it will be extremely slow, but none the less, it could be a viable option.
If the application is written in VB6 you might have to work with interopt.
i want to write a vb.net to let me connect to my hand punch . my hand punch has serial port that are connected to converter that convert the serial port to network , that converter has an ip addreess , this converter is connected to my network , how i can wirte a code that can let me be connected to my handpunch throug this converter and get a fucntion form my dll ?