Ok a friend helped me out, here's the jQuery that does what I want. I don't use one background image anymore but multiple div's, and the jQuery scrolls to their ID's.
$(document).ready(function(){
$("#dropdownlist").on('change',function(){
var project = "#" + $(this).val();
$.scrollTo($(project), 1000);
});
});
Principle:
<div id="workone">Work 1 content</div>
<div id="worktwo">Work 2 content</div>
<div id="workthree">Work 3 content</div>
<select id="dropdownlist">
<option value="workone">Work 1</option>
<option value="worktwo">Work 2</option>
<option value="workthree">Work 3</option>
</select>
Link to the scrollto jQuery download: http://flesler-plugins.googlecode.com/files/jquery.scrollTo-1.4.3.1-min.js
Thanks for the advices!