Strange: What you quote looks fine, and should work. Are you sure there is no overriding display: block !important somewhere?
But as my opinion, I’m going to say that for the love of God, just use a table. 🙂
Seriously. The main argument for not using tables in such situations is that they aren’t the right element semantically. But looking at that div-soup, you have to admit a <table> is the way more preferable construct, even if it’s not exactly tabular data you’re displaying.