Can you centre a Layer?

okay complete noob question, but I cant find the answer to this anywhere. I need an image to sit dead centre in any resolution of browser, lets say for example IE6 and IE7 800 and 1024. I need, as that screen size is changed, the image to be in the centre of whatever the screen resolution is changed to. If I use a table simple, I centre the table, place an image in it and presto. How do I get a layer to do likewise? How do I give it a location in the centre of a screen instead of having to specify a px or percentage distance from the left? Indeed, can I just attatch it to a table somehow?

Should add I am using DW and I am already aware of this solution: http://www.webmasterworld.com/forum83/5532.htm