Ok, I see what you mean now

I thought you just had three floated columns with content stacked in each column which is exactly what the drawing looks like.
You want a series of independent elements to line up as per your drawing but I don't think that's at all possible. I remember years ago trying something similar for two columns of just right and left floats and found it impossible. It may be possible with some of the new css3 column modules but I haven't played around with them yet as they keep changing the specs.
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