Issue with a menu system in wordpress using jQuery
jQuery(document).ready(function () {

//transitions
//for more transition, goto http://gsgd.co.uk/sandbox/jquery/easing/
var style = 'easeOutExpo';

//Retrieve the selected item position and width
var default_left = Math.round(jQuery('#lava li.selected').offset().left - jQuery('#lava').offset().left);
var default_width = jQuery('#lava li.selected').width();

//Set the floating bar position and width
jQuery('#box').css({left: default_left});
jQuery('#box .head').css({width: default_width});

//if mouseover the menu item
jQuery('#lava li').hover(function () {

    //Get the position and width of the menu item
    left = Math.round(jQuery(this).offset().left - jQuery('#lava').offset().left);
    width = jQuery(this).width();
    jQuery('#debug').html(left);
    //Set the floating bar position, width and transition
    jQuery('#box').stop(false, true).animate({left: left},{duration:1000, easing: style});
    jQuery('#box .head').stop(false, true).animate({width:width},{duration:1000, easing: style});

    //if user click on the menu
}).click(function () {

    //reset the selected item
    jQuery('#lava li').removeClass('selected');

    //select the current item
    jQuery(this).addClass('selected');

});

//If the mouse leave the menu, reset the floating bar to the selected item
jQuery('#lava').mouseleave(function () {

    //Retrieve the selected item position and width
    default_left = Math.round(jQuery('#lava li.selected').offset().left - jQuery('#lava').offset().left);
    default_width = jQuery('#lava li.selected').width();

    //Set the floating bar position, width and transition
    jQuery('#box').stop(false, true).animate({left: default_left},{duration:1500, easing: style});
    jQuery('#box .head').stop(false, true).animate({width:default_width},{duration:1500, easing: style});

});

<div id="lava">
                    <ul>
                        <!-- To show "selected" on the home page -->
                            <li<?php
                                    if (is_page('Home'))
                                    {
                                    echo " class="selected"";
                                    }?>>
                                    <a href="<?php bloginfo('url') ?>">Home</a>
                            </li>

                            <!-- To show "selected" on the About Us Page  -->
                            <li<?php
                                    if (is_page('about'))
                                    {
                                    echo " class="selected"";
                                    }?>>
                                    <a href="<?php bloginfo('url') ?>/about/">About Us</a>
                            </li>

                            <!-- To show "selected" on the Portfolio Page -->
                            <li<?php
                                    if (is_page('portfolio'))
                                    {
                                    echo " class="selected"";
                                    }?>>
                                    <a href="<?php bloginfo('url') ?>/portfolio/">Portfolio</a>
                            </li>

                            <!-- To show "selected" on the Blog Page -->
                            <li<?php
                                    if (is_home())
                                    {
                                    echo " class="selected"";
                                    }
                                    ?>>
                                    <a href="<?php bloginfo('url') ?>/blog/">Blog</a>
                            </li>
                            </ul>

                    <div id="box"><div class="head"></div></div>

<li<?php
                                    if (is_home())
                                    {
                                    echo " class="selected"";
                                    }
                                    else if(is_page('<?php the_title(); ?>/%postname%/')){
                                        echo " class="selected"";
                                    }
                                    ?>>
                                    <a href="<?php bloginfo('url') ?>/blog/">Blog</a>
                            </li>