130610 Floating Image Alignment

I need to add a FLOATING image to my CENTER aligned web-page (by floating image I mean something like a LAYER). When I tried to do this using ABSOLUTE positioning, it works, until you view on a lrger or smaller monitor. When I tried using RELEVANT positioning, it also worked, but left a blank space on the page in the area where the tag was placed. Can someone help me with a tag which will allow my floating image or layer to show in the same position regardless of screen size ... and without messing-up my site layout?