A fixed width width table (less than 760px wide) will display exactly
the same on any browser opened to at least 800px wide, no matter what
screen resolution is used. And wider fixed width tables will also be
the same, but with part cut off and a horizontal scrollbar to move to
the missing part.
Knowing screen resolution will not help, and in many cases will cause
even more problems. Consider that many users have high resolution
screens, but do not have their browsers open to full screen - a page
designed for 1280x1024 displayed in a browser opened at 800x600, with
screen res of 1280x1024, will give undesirable horizontal scrollbars..