function getLeaf(url) {
var splited=url.split('?');// remove all the parameter from url
url=splited[0];
return url.substring(url.lastIndexOf("/")+1);// return file name without domain and path
}  
jQuery.fn.extend({
enter: function() {//plugins creation
return this.each(function() {
var pth = $(this).find("img")[0];
//alert($(this).children().attr("href"));
if($(this).children().attr("href")==getLeaf(document.location.href)){// check that the link url and document url is same
$(pth).attr("src",pth.src.replace(/.gif/g, '_active.gif'));
} else{
$(this).hover(function(){
$(pth).attr("src",pth.src.replace(/.gif/g, '_active.gif'));// mouse over Image
},function(){
$(pth).attr("src",pth.src.replace(/_active.gif/g, '.gif'));// mouse out image
});
}
});
}
});
$(function(){  // Document is ready
$("#header a").enter();// call the function
});