active navigtion

Hi,

I have created my navigation which works fine. I would like to apply an active state to the list item depending on what category you are on. I know how to do this in css and html, but I’m new to php and I’m struggling a bit.

Please help :O)

<ul id="nav">

                 <?php $category_id = get_cat_ID( 'pensions' ); $category_link = get_category_link( 3 );?>

                 <li id="nav-pensions"><a href="<?php echo $category_link; ?>" title="pensions"><span>pension</span></a></li>

                 <?php $category_id = get_cat_ID( 'money' ); $category_link = get_category_link( 4 );?>

                 <li id="nav-money"><a href="<?php echo $category_link; ?>" title="everyday money"><span>everyday money</span></a></li>

                 <?php $category_id = get_cat_ID( 'mortgages' ); $category_link = get_category_link( 5 );?>

                 <li id="nav-mortgages"><a href="<?php echo $category_link; ?>" title="mortgages"><span>mortgages</span></a></li>

                 <?php $category_id = get_cat_ID( 'savings' ); $category_link = get_category_link( 6 );?>

                 <li id="nav-savings"><a href="<?php echo $category_link; ?>" title="saving and investments"><span>savings and investments</span></a></li>

                 <?php $category_id = get_cat_ID( 'protection' ); $category_link = get_category_link( 7 );?>

                 <li id="nav-protections"><a href="<?php echo $category_link; ?>" title="protection"><span>protections</span></a></li>

               </ul>