Try replacing pixels with %. Switch it to 50% and 50% and go from there. See how that works. If you're willing to go farther than that, as in replace your entire column code's I have a pretty good code for you that I use.
CSS
.leftcolumn {
position: absolute;
width: 100;
top: 0px;
left: 0px;
background-color: #32cd32;
}
.rightcolumn {
position: absolute;
width: 700;
top: 0px;
left: 100px;
background-color: #00ffff;
}
HTML
<DIV class="leftcolumn">
Contents of the left column.
</DIV>
<DIV class="rightcolumn">
Contents of right column.
</DIV>