When you use AJAX in ASP.NET, the calls are sent to the server asynchronously and will call back to the javascript you tell it to. This is all done without reposting the page (blinking). There are various AJAX libraries and samples, but since you did not say what version of ASP.NET you are using it is hard to point you to something that you can use directly. Here is a link to the AJAX samples on the website.
http://www.codeproject.com/KB/ajax/[
^]