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I'm not entirely sure I understand what you are meaning.
I think you are saying, "What makes blocks display in a top to bottom order, versus a left to right order on my site?".
If I understood you correctly, the answer is the XHTML and CSS of your theme.
Most themes are structured so that blocks will flow down. You order them by assigning weight in the Blocks admin. However, if you want your blocks to flow left to right, you're going to have 2 options. The easy (read lazy) way, or the right way.
The easy way is to use a table and do an if loop on the table cells. While this is the easiest to do, it is ugly and it is not even remotely what W3C standards specify, so I don't recommend it.
The hard, but proper way would be to do a div loop where the divs have a fixed width. You will be limited in the number of divs by the width of the browsing user's screen. Any divs that extend beyond will automatically start a new row. This will take some tinkering in your CSS to get it right, but it is doable.
If I've missed the mark, let me know and I'll try again.
HTH.
James
Insanity can be defined as "doing the same thing over and over and expecting different results."
Stupidity is not a crime. Therefore, you are free to go.