Get Users from Domain - IMP & URGENT

My Requirements are -
1.
string Domain = System.Net.NetworkInformation.IPGlobalProperties.GetIPGlobalProperties().DomainName;
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Get all users from this domain.

Display them in GridView and also insert those in SQL Server Table.
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2.
Consider any MNC (Say TCS, Infosys, IBM, etc).
For Example, take an MNC IBM.
IBM is in India, USA, etc and many other places.
Now,
How to get all the users of IBM ?? And display them in gridview ??
In short,
If I want to get all the users of my company, whether the user is in US, UK, India, where ever, how do I get them ??

I can get the domain from My Computer (in.abc.com).

But, how to get users of abc.com (IBM.com)



Please help.

This is on Urgent basis.