Hi Narayana;
I developed a PB Based Web Service that brokers the communication to Active Directory to perform many functions. One similar function is to verify that a user is part of an AD Group. I don't think that it would not take much effort to add the compliment feature of adding a user to AD into my original code. All the basic mechanics are there to be able to interact with AD in the PB Web Service. This might give you a great head-start by using the WS as your base for the Add User to AD feature.
Here s the URL for the AD based WS (which is free & open source) ... click here to download. Also, I gave an AD presentation on this topic at the last PB Conference. You can download the presentation from here.
HTH
Regards ... Chris