If you don't care so much about IE6 and IE7, the simplest answer is setting
display: table-cell;
on each of your columns.
Just check http://ie7nomore.com/css2only/table-layout/ for this pure CSS2.1 solution (both columns are contenteditable so you can easily add lines and lines of text in one and/or another column)
And no it isn't "using tables" as some may argue : the table
value of the CSS property display
renders the same way as a the HTML element table
but it's still the semantic of a div
(i.e. none) or whatever element it's applied to ;)
Then for IE6 and IE7, you can use conditional comments for a simple fallback (like applying background to one of the column and if the other is longer in some pages ... nevermind and forget it, it's old IE and your text is still readable)
Another method (a visual trick) is the technique of faux-columns