How Do I Drop Down Menus in the Header?

[LCN2007]

Here is my whole header.
Im wanting to turn the stuff in red into menus with additional dropdown items.

Thanks for your help.

<div id="wrap">

<div id="topnav"><img src="http://www.yoursite.com/forum/images/onlydev/misc/topnav_right.gif" class="fright" alt="" /><img src="http://www.yoursite.com/forum/images/onlydev/misc/topnav_left.gif" alt="" /><a href="http://www.yoursite.com/" onmouseout="MM_swapImgRestore()" onmouseover="MM_swapImage('topnav_home','','http://www.yoursite.com/forum/images/onlydev/misc/topnav_home_over.gif',1)"><img src="http://www.yoursite.com/forum/images/onlydev/misc/topnav_home.gif" name="topnav_home" id="topnav_home" alt="$vboptions[bbtitle]" /></a><a href="http://www.yoursite.com/forum/" onmouseout="MM_swapImgRestore()" onmouseover="MM_swapImage('topnav_forum','','http://www.yoursite.com/forum/images/onlydev/misc/topnav_forum_over.gif',1)"><img src="http://www.yoursite.com/forum/images/onlydev/misc/topnav_forum.gif" name="topnav_forum" id="topnav_forum" alt="$vboptions[bbtitle]" /></a><a href="calendar.php$session[sessionurl_q]" onmouseout="MM_swapImgRestore()" onmouseover="MM_swapImage('topnav_events','','http://www.yoursite.com/forum/images/onlydev/misc/topnav_events_over.gif',1)"><img src="http://www.yoursite.com/forum/images/onlydev/misc/topnav_events.gif" name="topnav_events" id="topnav_events" alt="$vbphrase[calendar]" /></a><a href="$vboptions[contactuslink]" rel="nofollow" onmouseout="MM_swapImgRestore()" onmouseover="MM_swapImage('topnav_contact','','http://www.yoursite.com/forum/images/onlydev/misc/topnav_contact_over.gif',1)"><img src="http://www.yoursite.com/forum/images/onlydev/misc/topnav_contact.gif" name="topnav_contact" id="topnav_contact" alt="$vbphrase[contact_us]" /></a><img src="http://www.yoursite.com/forum/images/onlydev/misc/topnav_mid.gif" alt="" /></div>

<div class="fright" id="nav">

<a href="http://www.yoursite.com/forum/garage.php" onmouseout="MM_swapImgRestore()" onmouseover="MM_swapImage('nav_garage','','http://www.yoursite.com/forum/images/onlydev/misc/nav_garage_over.gif',1)"><img src="http://www.yoursite.com/forum/images/onlydev/misc/nav_garage.gif" name="nav_garage" id="nav_garage" alt="Garages - Time Slips - Dyno Charts" /></a>

<a href="http://www.yoursite.com/classifieds/index.php" onmouseout="MM_swapImgRestore()" onmouseover="MM_swapImage('nav_classifieds','','http://www.yoursite.com/forum/images/onlydev/misc/nav_classifieds_over.gif',1)"><img src="http://www.yoursite.com/forum/images/onlydev/misc/nav_classifieds.gif" name="nav_classifieds" id="nav_classifieds" alt="Classifieds" /></a>

<a href="http://www.yoursite.com/forum/payments.php" onmouseout="MM_swapImgRestore()" onmouseover="MM_swapImage('nav_support','','http://www.yoursite.com/forum/images/onlydev/misc/nav_support_over.gif',1)"><img src="http://www.yoursite.com/forum/images/onlydev/misc/nav_support.gif" name="nav_support" id="nav_support" alt="Support the Community" /></a>

<a href="http://www.yoursite.com/forum/advertise.php" onmouseout="MM_swapImgRestore()" onmouseover="MM_swapImage('nav_vendor','','http://www.yoursite.com/forum/images/onlydev/misc/nav_vendor_over.gif',1)"><img src="http://www.yoursite.com/forum/images/onlydev/misc/nav_vendor.gif" name="nav_vendor" id="nav_vendor" alt="Supporting Vendors" /></a>

<a href="faq.php$session[sessionurl_q]" onmouseout="MM_swapImgRestore()" onmouseover="MM_swapImage('nav_faq','','http://www.yoursite.com/forum/images/onlydev/misc/nav_faq_over.gif',1)"><img src="http://www.yoursite.com/forum/images/onlydev/misc/nav_faq.gif" name="nav_faq" id="nav_faq" alt="$vbphrase[faq]" /></a>

<img src="http://www.yoursite.com/forum/images/onlydev/misc/nav_bottom.gif" alt="" /></div>