Cropping Background Image for Most Resolutions

[aquastream]

A newbie question - I setup a 1920x1080 image figuring that those dimensions would handle most PC monitors. In the very centre of this image is an important 1020x768 area which I want to show everytime somebody views the site - obviously it wouldn't display properly if they're a 800x600 user, but I'm figuring most people have gone past that by now. The rest of the background image though is extraneous, and I really don't care if bits of it are cut off depending on the person's screen resolution.

 

So the question is, how do I ensure that the image is shown from the centre rather than from the top left hand corner? Would I need some code to sense the screen resolution of their monitor and then have different versions for each, or is there a single HTML or whatever language command that will allow me to do this with a single image?

[haku]

Are you using in in image tags, or as a background image? If it's a background image, you can set this in your css:

 

background-position:center center;