I think the css problem is likely to be with the menu unordered list css, rather that with the leftcolums1 div css.
Not sure, but look at your:
ul#cssmw1 li {
background-image: none;
padding: 0 0 0 0;
position: relative;
white-space: nowrap;
z-index: 99999;
position: relative;
}
Try removing the first 'position: relative;' property (you have two!) , test your page, and then try removing the second one.
Otherwise, if you could upload your menu temporarily and provide a link to it, it would be easier to investigate.