How do I set max <td> height?

I'm using mysql with PHP and the length of each td depends on how many rows are returned. I have 4 's per row and I want the max height to be a certain amount. I can set the height of each to a certain length but if the number of rows returned is less than the max height, I don't want to display all that extra space. I was wondering if there was a way to set the max height for the row without going through each first, finding out the max, and after that, go back and print each . And a side question, is there a way to automatically center the scroll bar?