Hi Kidthnk1,
Before we send detailed steps on our Active Directory Web Service, do you have access to a server running IIS 5.1 or greater? You'll need that to install the Web service.
If you have InfoPath 2007, you can get the username without writing code and compare this to the list in the dropdown. This is easier than installing our AD Web Service, but there are some caveats - i.e. you can't get as much information and it doesn't work when the user is logging in remotely from a computer that has not been joined to the domain. However, it's pretty simple.
Patrick Halstead
Project Manager at Qdabra