Only after something is typed inside the textbox, The button should be enabled.

Copy the following code in the notepad and save it as test.htm and then run it.
<form name="form1"> <input type="text" name="iserod" id="userid" onKeyUp="enableBn1();"/> <input id="button1" type="button" disabled="disabled" value="Button1"> </form> <script> function enableBn1(){ if(document.form1.userid == ""){ document.form1.button1.disabled = true; } else{ document.form1.button1.disabled = false; } } </script>

Ajax code for Check Availability of User ID

<form name="form1"> <input type="text" name="userid" id="userid" /> <input id="button1" type="button" value="check availability" onclick="sendLamens();"> </form> <div id="label1"></div> <script> function sendLamens(){ if(window.XMLHttpRequest) { lamens = new XMLHttpRequest(); } else if(window.ActiveXObject){ lamens = new ActiveXObject("Microsoft.XMLHTTP"); } lamens.open("POST", "test1.asp", true); lamens.onreadystatechange = fetchFromLamens; lamens.setRequestHeader("Content-Type", "application/x-www-form-urlencoded"); lamens.send("userid=" + document.form1.userid.value); } function fetchFromLamens(){ if(lamens.readyState == 4){ if(lamens.status == 200){ document.getElementById("label1").innerHTML = lamens.responseText; } else{ document.getElementById("label1").innerHTML = "error"; } } } </script> <!-- The readyState propery is used to know whether the reply from the web server has been received or not. : 0 : uninitialized 1 : loading 2 :loaded 3 : interactive 4 : completed Suppose, the client has received the reply. If the reply is OK then it is 200,and if the received reply is error message then it is 404 The OPEN method sets the different values such as the type of request(GET or POST), the URL, if it is asynchronous(true) or synchronouse(false). -->

<% x=Request("userid") If x="lamens" Then Response.Write("Yah!Lamens is available") Else Response.write("Why dont you try lamens") End If %>