The position: absolute will take its position from the page or screen window normally, which is why your bottom image is at the bottom of the page.
However, if the containing div has position: relative, anything that is position: absolute inside it will take its position from the div dimensions and not from the page/screen dimensions.
This works as image 1 is at the top of the div and image 2 is at the bottom (I've just tested it):-
<div style="position: relative; width: 400px; height: 500px;
border: 1px solid black;">
<img style="position: absolute; top: 0; left: 200px;"
src="image1.jpg" alt="image 1">
<img style="position: absolute; bottom: 0; left: 300px;"
src="image2.jpg" alt="image 2">
</div>
See
http://www.wickham43.supanet.com/tutorial/divboxes.html
Code downloaded to my PC will be deleted in due course.
WIN7; IE9, Firefox, Opera, Chrome and Safari for Windows; screen resolution usually 1366*768.
Also IE6 on W98 with 800*600 and IE8 on Vista 1440*900.