You need to use a javascript sniffer to find the screen resolution and then use different stylesheets for the different resolutions.
Google: screen resolution detection javascript.
This is one link I looked at:-
http://www.pageresource.com/jscript/jscreen.htm
The example sends the viewer a different html PAGE if he has a small or large screen resolution but different code can also divert to a different stylesheet from the same page.
Ask on the javascript board how to code it properly.
Remember that it will tell you what screen resolution a viewer's browser is set at but not what window size he is using. He may have a screen resolution of 1280*1024 but always use a smaller window. People with 1600*1200 resolutions often split their screens vertically into two 800px wide windows.
Code downloaded to my PC will be deleted in due course.
WIN7; IE9, Firefox, Opera, Chrome and Safari for Windows; screen resolution usually 1366*768.
Also IE6 on W98 with 800*600 and IE8 on Vista 1440*900.