function loginUser()
{
    var client = new XMLHttpRequest();
    
    client.onreadystatechange = function()
    {
        if(this.readyState == 4)
        {   
            if(this.status == 200)
            {
                if(this.responseText == '')
                {
                    // redirect to their wishlist after registering
                    window.location = 'do/mine';
                }
                else
                {
                    // parse the error code passed back
                    var errorCode = parseInt(this.responseText);
                    
                    if(errorCode == 0)
                    {
                        alert(this.responseText);
                    }
                    
                    // check for error code
                    if(errorCode == 1)
                    {
                        // make username field red to indicate error
                        document.getElementById('login-username').className = 'error';
                        
                        // make password field red to indicate error
                        document.getElementById('login-password').className = 'error';
                        
                        // display error message
                        alert("Wrong username or password!");
                    }
                }
            }
            else
            {
                alert("Hm... error! " + this.statusText);
            }
            
            // clear the password field
            document.getElementById('login-password').value = '';
        }
    };
    
    // reset any error fields
    document.getElementById('login-username').className = '';
    document.getElementById('login-password').className = '';
    
    var username = document.getElementById('login-username').value;
    var password = document.getElementById('login-password').value;
    
    var url = 'login.php';

    var data = 'username=' + escape(username) + '&password=' +
               escape(password)
    
    client.open('POST', url, true);
    
    client.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
    
    client.send(data);
}