[TECK]

Cool find, Nutz.
There is no need to use hooks for this, it's more like a template mod.
Open google.js and add this line at the end of the file:
window.onload = init_google;

Then open your headinclude template and add this line:
<script type="text/javascript" src="clientscript/google.js"></script>

I never liked to use body onload= atributes...
Now, the onload function should load your code only after the hole page is fully loaded... and some of us find this bad.
If you want to complicate your life, you could simply create a script that will make sure it loads the javascript code, before the page is loaded.

For example:

function init_google()
{
	// Avoid statement ‘Element Ready’ to be displayed twice
	if (arguments.callee.done)
	{
		return;
	}
	arguments.callee.done = true;

	var pattern = /google\./i;
	if (pattern.exec(document.referrer) != null)
	{
		var url_parts = document.referrer.split('?');
		if (url_parts[1])
		{ 
			var url_args = url_parts[1].split('&');
			for(var i = 0; i < url_args.length; i++)
			{
				var keyval = url_args[i].split('=');
				if (keyval[0] == 'q')
				{
					go_google(decode_url(keyval[1]));
					return;
				}
			}
		}
	}
}

if (document.addEventListener)
{
	document.addEventListener('DOMContentLoaded', init_google, null);
}
else
{
	addLoadEvent(init_google);
}
window.onload = init_google;

This was done off my mind, not tested, so feel free to play with it.