Funzione onclick per i tasti attivi header nav bar

[troy]

Ciao a tutti, qualcuno sa darmi indicazioni sul codice da inserire per la funzione "onclick" o equivalente, per cambiare il background ai tasti "attivi" della navigation bar ? Attualmente il codice è il seguente:

Grazie.
Stefano

</table>
<table border="0" width=480 cellspacing="4" cellpadding="0" align=center >
<td align="middle" valign="bottom"><div id="tabsJ">
<ul>
<li><?php echo '<a href="' . tep_href_link(FILENAME_DEFAULT, '') . '">' . "<span>" . ('Home') . '</a></span>'; ?></li>
<li><?php echo '<a href="' . tep_href_link(FILENAME_LOGIN, '', 'SSL') . '">' ."<span>".('Log in') . '</a></span>'; ?></li>
<li><?php echo '<a href="' . tep_href_link(FILENAME_CREATE_ACCOUNT, '', 'SSL') . '">' . "<span>" . ('My Account') . '</a></span>'; ?></li>
<li><?php echo '<a href="' . tep_href_link(FILENAME_CHECKOUT_SHIPPING, '', 'SSL') . '">' . "<span>" . ('Checkout') . '</a></span>'; ?></li>
<li><?php echo '<a href="' . tep_href_link(FILENAME_CONTACT_US, '') . '">' . "<span>" . ('Contact us') . '</a></span>'; ?></li>
</ul>
</td>
</div>
</table>


CSS:

#tabsJ {
float:left;
width:939px;
background:#ffffff;
font-family: Tahoma;
font-size:100%;
font-weight: bold;
line-height:normal;
border-bottom:14px solid #91063d;
padding-top:5px;
}
#tabsJ ul {
margin:0;
padding:10px 10px 0 0;
list-style:none;
}
#tabsJ li {
display:inline;
margin:0;
padding:0;
}
#tabsJ a {
float:left;
background:url("images/tableftJ.gif") no-repeat left top;
margin:0;
padding:0 0 0 14px;
text-decoration:none;
}
#tabsJ a span {
float:left;
display:block;
background:url("images/tabrightJ.gif") no-repeat right top;
padding:9px 24px 9px 9px;
color:#333333;
}
/* Commented Backslash Hack hides rule from IE5-Mac \*/
#tabsJ a span {float:none;}
/* End IE5-Mac hack */
#tabsJ a:hover span {
color:#91063d;
}
#tabsJ a:hover {
background-position:0% -31px;
}
#tabsJ a:hover span {
background-position:100% -31px;
}