You shouldn’t really be using ‘valign’ it’s a deprecated attribute, presentation is handled by CSS.
The reason that valign isn’t working for you is precisely because CSS has been used to apply a vertical-align: middle; to that cell.
You need to use a debugging tool such as Firebug for FireFox to allow you to examine the applied style/ rulesets for elements then you would be able to see what was affecting what.
BP default.css states that all table cells should be vertical-align: middle, you will need to adjust that specifically for that cell either by adding a class to style on or using descendant selectors.
