Google Maps Api v3 custom InfoWindow - "google is not defined" error

trying to create custom infowindows in my application that is based on google maps.

next example is one of my base points for development:

http://gmaps-samples-v3.googlecode.com/svn/trunk/infowindow_custom/infowindow-custom.html

problem is that whatever i use this or some other example, in forefox's firebug i'm getting error

google is not defined
InfoBox.prototype = new google.maps.OverlayView(); 

can you help me how to solve this, i can not continue my work with开发者_StackOverflowout custom infowindows.....

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my mistake - i did not include properly google map api library - i included infobox.js before http://maps.google.com/maps/api/js?sensor=false