write to username and password fields in a browser to log in

Hello All,

I am just trying to create a GUI window executable in VS C# .NET 2010. I want to perform automation to log into facebook, gmail, hotmail and other sites i want by clicking a button on the GUI.

        private void facebook_Click(object sender, EventArgs e)
        {
            string target = "www.facebook.com";
            Process.Start(target);  
        }

I can open up the target window.. I just don't know how to write to email and password fields and log in automatically. its just something i wanna do for myself.. I wanna treat it like a standalone service and when I give in username and passwords to gui then i can log into websites with a click... instead of opening up browsers and logging in from there..

Please let me know if its possible and provide some examples...

Thanks a bunch!