>I need to create a login screen that accepts a login name and password. Then I need to verify that the login and password are valid for a domain user. I was told there is some API call that I can make to do this. Can someone help me figure out how to call this API? Thank you for your help.

Take a look at the following:

Verify NT Password File #9875

You may also contact Paul Vlad Tatavu. He has done an extensive NTUser class which does all of that.