uses shellapi; 

procedure InstallScreenSaver(const FileName: string); 
begin 
{ Set this screensaver as default screensaver and open the properties dialog} 
ShellExecute(Application.Handle, 'open', PChar('rundll32.exe'), 
PChar('desk.cpl,InstallScreenSaver ' + FileName), nil, SW_SHOWNORMAL); 
end; 
procedure TForm1.Button1Click(Sender: TObject); 
begin 
InstallScreenSaver('c:\YourScreenSaverFile.scr'); 
end;