Hi!
If you ready to write a DLL or COM server using C, then this article can help you: "Q180548 - HOWTO: Validate User Credentials on Microsoft WinNT and Win95".
Next article also may be useful: "Q197236 - HOWTO: Programmatically Log On to a Network on Win95/Win98".

>I think I was a bit vague in my question. The thing I want to do is when the user enters username and password in our application I want to validate this in the domain.