Hi Gaurs,
We created the Active Directory Web service (see Downloads) to solve you problem. You have to install it on a server on you network , but it will allow you to prepopulate the username without writing any code. You can get the user's logged-in alias if you use code, but there is no way to get the actual user's name without calling Active Directory (which is what our Web service does). It's only ~$20 and it is one of our most popular downloads. If you have any questions, please see the Premium Downloads forum where there are several good posts on how to use the Web service. It also comes with instructions on how to setup and use.
Cheers!
Patrick Halstead
Project Manager at Qdabra