Try this..
Locate vbulletin-chrome.css by searching in the templates.
You should then easily find the css and where it says:
Then find the hight in pixels, and it should read something like "min-height:100px;" (if it is 100 pixels), so all you need is to increase that number.
NOTE: Before you do that, I would suggest backing up the vbulletin-chrome.css in notepad until the results are shown to be ok:up: