Looks like you're using flexible squares, so try s2flexisquares that's what I've been using. There are a whole bunch of different tutorials with overrides and such to customize your header, most of them are pretty straight forward, just copy and paste the codes, but should you have any questions just go ahead and ask, they're very quick about answering questions.

It'll just be difficult to show you how to do it in one comment.

Try this (http://community.livejournal.com/s2flexisquares/130476.html) tutorial, although there are a few different ways of doing it.