A: The Microsoft.Exchange.WebServices.dll file is part of the Exchange Web Services Managed API.
Download the Exchange Web Services Managed API at the Microsoft download website. After it's installed, just copy the file from the installed directory, C:\Program Files\Microsoft\Exchange\Web Services\1.1, by default.
Answers to all your Windows, systems management, Exchange questions--and more--can be found at John Savill's FAQs.