Asp.net - Using .aspx Page As Ajax Event Handler?

For several days now I've been messing around with Ajax calls using different combinations of javascript, ASP controls, and regular controls. I've gotten a bit of understanding about what's going on, but using ASP controls still hides too much of the machinery, and I want to have a deeper understanding. With that aim, can anyone tell me why the following setup doesn't quite work?I have a file "Testy.aspx" with the following:[code].....

So, I hoped to make my .aspx file do double-duty both as the regular-page request handler as well as the Ajax request handler. However, when I click the button ("baroo") to generate the Ajax request, the result that ends up written back to the "testytext" div is the raw html for the entire page, as if under normal request conditions. Clearly, my attempt to override the page request by making the code-behind implement IHttpHandler and supplying an "Overrides Sub ProcessRequest" method is not working. The server is still treating the Ajax request as a normal request, and in fact my own "ProcessRequest" method is never even called.Is it possible to build a page/handler like this? How can I intercept the incoming request from the client and respond accordingly?This is how Ajax works, right? So it must be possible.Again, I'm deliberately doing this as an excercise to avoid the use of "magic" ASP controls like UpdatePanels,