The search box is displayed as part of dirbar.php in the upper right on most Physpics pages. Initially gray, but comes alive when it is clicked to get focus. The appearance is managed by evemt handlers for onblur/onfocus that call scripts.js.searchblur/searchfocus. When the arrow is clicked or return is typed, Google is invoked with a query liike this:

http://www.google.com/search?domains=physpics.com&num=50
   &ie=utf-8&oe=utf-8&sitesearch=physpics.com&q=theQuery

where the domains and sitesearch values are from php's $_SERVER['SERVER_NAME'];

The search response is a google page and it replaces the current browser tab.