Ajax the old way

Question

I would like to know how a script manager manages to execute a button click, Dropdownlist selectedindexchange etc.. events without marking the method a [WebMethod] and making it static Does this mean i will be able to call a method using Ajax on button click ? Also can some one provide me a example which posts data to ASP.NET webpages using Traditional XMLHttpRequest and How do i recieve the data sent in my CodeBehind page.