There are already heaps of posts on this topic in this forum, do a search.
Don't use absolute positioning to align an element in the body to the centre, if you looked at it in a smaller or larger res it won't be in the centre.
What most people do it have a container centred in the middle of the page, then have everything aligned left inside this container div.
Then if you want anything inside this to align centre make an extra class and have this align centre and it will align centre in the container div, therefore in the centre of the page.
Let's say you want to put another image or text positionned somewhere near the 3/4 of the image "blah.gif", wouldn't you have to use absolute positioning?
Hard to say for sure without a good visual idea of what you want, but from the description I'd guess that either you'd use relative positioning or perhaps just tweaking the margins or padding of the element you want positioned.
"Please give us a simple answer, so that we don't have to think, because if we think, we might find answers that don't fit the way we want the world to be."
~ Terry Pratchett in Nation
But even if I tweak your margin or padding, the image won't be on top of the first one... I'm getting more confusing...
If you have a look at the website I did, which is my first website in CSS, there's the 'latest news' image. Then, on top of it, there's another DIV for the text, then another DIV for the blue cylindric images, and finally a DIV for the 'Read more''s. The four DIVs are using absolute positioning.
I know it's all messy, but that's the only way I know for the moment.
So, How would this same positioning be presented with another CSS method?