Unexpected space between floated divs

Hi, can you help me with this site?

http://mszp20.hu/new/index.php

I'm using a zen-based custom layout. As you can see, I have 2 columns of divs in the content area, every odd/even floats to left/right and they have 50% width.

My problem is that some of the divs which are supposed to float left, don't do it, instead they stay on the right where they should be without floating.

It's like they don't have enough space to float to the left... That would still be OK, the exact "post flow" isn't important at this site, but when they don't float to the left, a vertical space is inserted to the place where they should be located.

How can I eliminate this unnecessary space? Or if it's solvable, how can I make all the elements float where they are supposed to?

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More:
On another forum, I got this answer:

"You should not try and rely on luck to get this positioned the way you want, I'd sort this out into columns instead of having everything lined up and floated. Work that right column into 2 columns."

My problem with this, is that I can't put them into two separate columns with Drupal. Currently I'm arranging them using the "dynamic" id they get by showing on the frontpage. I've tried several methods, but I'm just simply not enough proficient with Drupal/PHP to solve this :(

Can someone describe a method for separating every even/odd teaser div on the frontpage into two separate divs inside the content-area div?

Please don't just say "use Views", because I fought with that module for several days because of a different reason, and I can't make it behave the way I want... It's just too complex and alien for my thinking. Or if it's only solvable by that, please write down the steps like you would for a dummy :D

Thanks for any help!! :)

(PS: I hope I posted this to the right forum.)