If you want to dynamically load google's libraries, you should check out google's autoloader:
http://code.google.com/apis/ajax/documentation/#AutoLoading
It works quite nicely, but be careful if you use the autoloader wizard.
http://code.google.com/apis/ajax/documentation/autoloader-wizard.html
there's a bug for the c&p code that tripped me up:
http://code.google.com/p/google-ajax-apis/issues/detail?id=244
Also I found that for some of google's libraries, if I try to asynchronously load scripts (like yours) that if I don't specify some of the optional parameters (language, callback, etc. -- even with an empty string), I'll see the behavior that you're seeing.
Edit: went ahead and tested it. Your solution here:
http://pastie.org/486925