Google Analytics Cross Domain Tracking
If you control multiple domains and/or have multiple alias’ then in order to track visitors across them, you must modify the Google Analytics tracking code:
<script type="text/javascript">
var gaJsHost = (("https:" == document.location.protocol) ? "<a href="https://ssl/" target="_blank">https://ssl</a>." : "<a href="http://www./" target="_blank">http://www.</a>");
document.write(unescape("%3Cscript src='" + gaJsHost + "<a href="http://google-analytics.com/ga.js" target="_blank">google-analytics.com/ga.js</a>' type='text/javascript'%3E%3C/script%3E"));
</script>
<script type="text/javascript">
var pageTracker = _gat._getTracker("UA-12345-1");
pageTracker._setDomainName("none");
pageTracker._setAllowLinker(true);
pageTracker._trackPageview();
</script>
By adding what is bold will allow you to track across multiple domains.