Whether you are aware of it or not:
Your page is in violation of Dynamic Drive's usage terms (http://www.dynamicdrive.com/notice.htm), which, among other things, state that the script credit must appear in the source code of the page(s) using the script. Please reinstate the notice first.
As that is AnyLink CSS Menu:
http://www.dynamicdrive.com/dynamicindex1/anylinkcss.htm
As to your question -
Generally, you cannot put the drop downs inside other positioned elements, sometimes not inside static elements (depending upon their attributes, parents, etc.). They can go as the first thing after the opening body tag, and usually will work well there. Move this:
<div id="community" class="anylinkcss">
<a href="iframes/gb.php" target="content">Guestbook</a>
<a href="iframes/newsletter.php" target="content">Newsletter</a>
<a href="iframes/download-area.html" target="content">Download Area</a>
<a href="iframes/links.html" target="content">Links</a>
<a href="iframes/win-a-ticket.html" target="content">Win A Ticket</a>
<a href="iframes/crew.html" target="content">Crew</a></div>
<div id="booking" class="anylinkcss">
<a href="artists/index.php/overview/all" target="content">All Booking's</a>
<a href="artists/index.php/overview/1" target="content">DJ's & MC's</a>
<a href="artists/index.php/overview/2" target="content">Live Act's</a>
<a href="artists/index.php/overview/3" target="content">DanceCrew's</a>
<a href="artists/index.php/overview/4" target="content">Dance Act's</a>
</div>
<div id="events" class="anylinkcss">
<a href="events/index.php/next_events" target="content">Next Events</a>
<a href="events/index.php/last_events" target="content">Last Events</a>
<a href="partyshots/index.php/overview" target="content">Partyshots</a>
</div>
to here:
<body style="overflow-x:hidden; overflow-y:auto;" onload="MM_preloadImages('img/menue/01-home-r.jpg','img/menue/02-comm-r.jpg','img/menue/03-bookings-r.jpg','img/menue/04-events-r.jpg','img/menue/05-contact-r.jpg','img/menue/06-impressum-r.jpg')">
<!-- Put drop downs below here -->
<!-- End drop downs -->