AutoIT :-

@Test
public void FileAttachement() throws Exception

{
driver.manage().timeouts().implicitlyWait(9, TimeUnit.SECONDS);
driver.get("http://seleniumsubbu.blogspot.in/");
driver.findElement(By.id("edit-submitted-uploadfile-upload")).click();

Runtime.getRuntime().exec("C:\\Users\\chinna\\Desktop\\AutoIT\\Fileupload.exe");
}