I know this is over a year old but I am assuming this is what you want to do:
rdp.Server = "Server";
rdp.UserName = "Username";
rdp.Domain = "Domain";
IMsTscNonScriptable secured = (IMsTscNonScriptable)rdp.GetOcx();
secured.ClearTextPassword = User.Password;
rdp.AdvancedSettings8.ConnectionBarShowMinimizeButton = false;
rdp.AdvancedSettings8.ConnectionBarShowPinButton = false;
rdp.AdvancedSettings8.ConnectionBarShowRestoreButton = false;
rdp.AdvancedSettings8.EnableWindowsKey = 0;
rdp.AdvancedSettings8.RedirectClipboard = true;
rdp.AdvancedSettings8.RedirectDrives = true;
rdp.AdvancedSettings8.RedirectPrinters = true;
rdp.AdvancedSettings8.SmartSizing = true;
rdp.SecuredSettings3.StartProgram = "LaunchApp Path";
rdp.Connect();
In addition follow what @Hans Passant suggested above..