I like fluid and "responsive" layouts that re-size with browser window size so, therefore, use % percentages. See for instance http://www.josephdenaro.com
Using a (naughty! No,NO!) <table> layout is not a sin (if it works). A fixed 3-column layout (without any floats) might be your answer. When figuring widths, remember the CSS box model and calculate right- and left-side padding, margin and border (that's x2 ) plus the content width (add some breathing space too). Then create your overall containing <div> (which I called WRAP) with a width great enough to encompass the inner 3-columns. You can then calculate your middle and right <div> margins to clear the columns to the left.
Humgh! What I'm finding when searching for 3-column fixed CSS layouts, such as http://www.csstutorial.net/2010/04/3-column-layout/
, use floats.
Think the main thing is to establish overall wrapper div that is wide enough. Also don't let that right-side Google ad squeeze out your main content.