3 colums in equal lenght

Hello,

I've got 3 colums on my website. I want all of them to be almost equal in
lenght ( I may be a little bit different, but not to much). I'm now
generating a PHP website where one colum is sometimes a lot longer then the
other!

I've got 5 to 15 articles from different sizes to display on the website,
how can get the three colums almost even in lenght??

The articles may be placed random on the site.

thnx,

PRCR