Write an post method either in ajax or jquery which will work in all browser(old version and latest version)?

I think using Jquery will be just fine and support all browsers including IE6:

http://www.w3schools.com/jquery/jquery_ajax_get_post.asp

http://www.w3schools.com/jquery/jquery_ref_ajax.asp

The JQuery syntax is wrong

Try this

$.post(

"submit.php",

{username:username,password:password},

function( data ) { alert(data); }

); 

Also the variables that recieve these post data in submit.php must have same names as mentioned here (i.e username and password)

Look up this tutorial - http://a100websolutions.in/ajax-php-database-update/

You can learn it from following URLs:

• http://api.jquery.com/jQuery.post/
• http://api.jquery.com/jQuery.ajax/
• http://www.w3schools.com/jquery/jquery_ref_ajax.asp
• http://www.w3schools.com/jquery/ajax_ajax.asp

This could be done using jQuery like this:

$("#form_id").submit(function(){

$.ajax({

data: $(this).serialize(), //serialize the form data to be sent

url:'submit.php' //the target

type:'post' // method of the form wether get / post

success: function(dataFromBackEnd){

$(body).appened(dataFromBackEnd);

}

error: function(errorMsg){

alert(errorMsg);

}

});

return false;

});

If you stick to jQuery then it handles all browser related worries. That is why jQuery was born in the first place.