On the SitePoint PHP blog there's a recent post from Craig Buckler showing how to split up your WordPress content into two or more columns quickly and easily.

WordPress is a great CMS, but implementing some features within your theme can require a little lateral thinking. The content for your page or post is usually output by the theme code using a single function call. But what if you need to split the content into two or more blocks? That might be necessary if your theme requires multiple columns or sections on the page.

There's a built in call WordPress includes, "get_the_content", that returns the content rather than just echoing it out. With this handy function giving you just the content, you're free to split up the content however you want - on certain tags or as they suggest, using the "more..." tag and a few modifications to a few other scripts to split it out into DIV blocks.