Have you registered the dlls? If they are not registered you will not able to access their functions.
I cannot speak for the Delphi libraries as I have no experience there but you should be able to access the VB6 dlls using interop.
Chapter 9 of this free book from Microsoft should help you.
http://msdn.microsoft.com/en-us/vstudio/ms788236[
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I know this is not a copy this code into your project answer, but going through the material should go a long way in providing the solution you seek and more.