The user hash needed to be a SHA256 hash of the users email address and the unique "salt" or secret key provided by intercom.io on a user account basis.
The problem was that I'm using Vbscript/classic ASP so was having trouble sorting this out with the limited VBScript library.
The solution was found courtesy of:
Basically you create a stand alone file called sha256.wsc that lives in the same directory as the function - then pass in the appropriate variables.
The contents for sha256.wsc follow at the end of the post. Good luck and happy coding