You can achieve it like this:
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.2.6/jquery.min.js"></script> <script> window.jQuery || document.write('<script src="/path/to/your/jquery"><\/script>'); </script>
This should be in your page's
<head> and any jQuery ready event handlers should be in the
<body> to avoid errors (although it's not fool-proof!).
One more reason to not use Google-hosted jQuery is that in some countries, Google's domain name is banned.