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In Blocks you'll see several radio buttons that indicate where on your page the blocks will sit. They are in order of left column, left center, center, right center, and right column. First, change the settings to center. After you submit your changes, click on the edit link for the block you want to change the settings on. There is a scroll box next to "Visible in". Select what pages you want the block visible in, then click submit. Now, when you go back to the Blocks admin page, the block's options won't be visible. This is because the blocks admin page shows only the blocks visible in either All Pages, or Top page. To view your settings for a particular page, click on the drop down box next to "Show blocks visible in" and select the appropriate page.
Hope this helps.
EDIT: Yeah, and what ChadK said too.