It will hardly be just some DLL.
You can use the library provided in this CodeProject article:
sharpSsh - A Secure Shell (SSH) library for .NET[
^].
Please see also:
http://bit.ly/YGJiWi[
^].
You need some available or your own implementation in the form of a library; certainly the open-source, then you can created a DLL by yourself. Most likely, the implementation will be in C or C++, but you won't need to know all the detail about these languages except DLL export.
You can even look for VB6 implementation:
http://bit.ly/YGJQeM[
^].
But I won't recommend messing with VB6; please see my comments to the question.
—SA