penders - 12:19 am on Jun 28, 2011 (gmt 0)
@Kickedout - There is nothing wrong with that last DOCTYPE you posted, so any validation error you are getting must be related to something else. What error are you getting?
I've just been having a bit of a play, using your absolutely positioned DIV in a page with/without a DOCTYPE, an invalid DOCTYPE, forcing quirks mode in IE8, etc. and it works every time - I can't break it! The DIV is positioned at (285px, 31px) in IE8, IE7, Firefox 3.6, Chrome and Opera.
So this leads me to think there is something else 'non-simple' about your page that is causing this? You say you are still getting validation errors...