<a href="shows.php?show=$tourdate_id" target="_blank" onclick="window.open('shows.php?show=$tourdate_id','Show','width=300,height=200,toolbar=no,location=no,status=no,menubar=no');return false">Link</a>
As you can see, opening a new window like that will require some Javascript. I decided to code it in a way such that if a user doesn't have Javascript enabled, they can still follow the link (it will open in a new window to be handled by the browser). Doing this also allows search engines to make sense of where the link goes.