I'm no expert at CSS, so I usually have to muck around with it until I find a combination that works. Save a copy of your stylesheet, then try various combinations of float on those divs. I've had luck floating the first column left, no float on the second, and float the third column right. The second column will sometimes just slip into place. It depends on the order they are being called into the template.
Plus you might have too much total width for all three columns to fit in the wrapper that contains them all. If your page is 950 pixels wide (for example) the total of the widths of the three columns, plus their padding, borders, and margins has to be less.
If you save a backup, you really can't break anything by trying.