Try adding this to your style.css
.post{clear:both;}

where in the style.css does that go? Sorry, still learning css.

Oh, and is that in the template's style.css or the one you can place in the media folder to add custom css?

EDIT: Nevermind, I added it to the template's css just at the very bottom and it worked!. thanks very much!

can you explain to me what this did and why it needed to be done?

I didn't look at your CSS too closely, but I imagine that there are a few float:lef, float:right statements for bits of the post layout structure.
Those floats need to be cleared before you start floating them in a following post again or good browsers will bite you and bad browsers will let things go until it really hits the fan :)