CSS3 has a solution, but it is not standard yet and won't work in older browsers here is a link http://www.css3.info/preview/multi-column-layout/.
Possibly the best idea is to use javascript somehow. Put all the text in the first column and test the height then move portions of the text over to the next column until you have equal columns or until the first column is at a desired height.
Another method is to have predefined proportions eg(2/3 in the first column and 1/3 in the second). Then split the text based on the proportions using character count. This won't be exact and you could use a method similar to the one above to find exact width based on overflow properties, but the characters should average out to be the correct length.
This method is pretty simple and would look like
var txt='Column text...';
var len=txt.length;
var chars=Math.floor(len*.67);
//Assuming you want 2/3 of the text in the first column
document.getElementById('col1').innerHTML=txt.substring(0,chars);
document.getElementById('col2').innerHTML=txt.substring(chars);
//Notice that this could split in the middle of a word so you would need to do
//some checking for the nearest space and the change the break to there.
//Also you could then use the previous method to adjust it if you want something really accurate