my question is about validation using php. i am validating a username which a user would enter and clicks on a image to find

if that username is available. example if a user enters abc#123 php file is reading this value as abc ONLY which i do not

want instead the php file should read as abc#123. follow is the sequence of pages. please advice the solution.

first page = register.php here a user enters a username and clicks on an image to find out if the username is available or

not. using a javascript function of onclick i am reading the value entered in the form in javascript as
=============================================
var useri = document.registrationform.username
var valueofuseri = document.registrationform.username.value

var recui = /^\s{1,}$/g;

if ((useri.value==null) || (useri.value=="") || (useri.length=="") || (useri.value.search(recui))> -1)
{
alert("Please Enter a User Name")
return false
}

window.open("checkusernamei.php?theusernameis="+valueofuseri, "titleforavailabilityi", "width=680,  height=275, status=1,

scrollbars=1, resizeable=yes");

============================================

second page = checkusernamei.php = this file uses GET to read what was entered in the form.
============================================
$username = $_GET["theusernameis"];

if( $username == "" ||  !preg_match("/^[a-z0-9]+(?:_[a-z0-9]+)?$/i", $username) )
{
echo "username is blank or has special characters";
}
============================================
the # sign is being ignored only if the image is clicked in order to check the username, if the user enters abc#123 and

clicks the submit button without clicking on the checkuser image button then my php validation for username shows an error

message.

==============================================================
if( $username == "" ||  !preg_match("/^[a-z0-9]+(?:_[a-z0-9]+)?$/i", $username) )
{ echo "display error message for username"; }
==============================================================
now the problem is with clicking the image only and passing using GET method how can i fix this problem.

please advice.

thanks.