Check Wheather User Data Exists in Database without PageLoad

Hello,

         I am a newbie to jQuery, I want a Simple jQuery Function Which can Detect Wheather the enter name/id/data exists in the database. I want the code to be straight forward jQuery function on the textbox .keyup() which has a web method inside the cs page, for which I don't have to use any external class file or web services (any external additional class files).

if the data exists alert('Data Exists')

else

 alert('Data Available')

 Please Help...