Sometimes you need to use many Analytics site profiles to track the same information, for any reason. One instance is using tools like SEO Position Plus which may require a profile of its own.
Here's one way to do it with the new tracking code (not the legacy tracking, for that see this thread).
<script type="text/javascript">
var gaJsHost = (("https:" == document.location.protocol) ? "https://ssl." : "http://www.");
document.write(unescape("%3Cscript src='" + gaJsHost + "google-analytics.com/ga.js' type='text/javascript'%3E%3C/script%3E"));
</script>
<script type="text/javascript">
try {
var pageTracker = _gat._getTracker("UA-xxxxxxx-1");
pageTracker._trackPageview();
var pageTracker2 = _gat._getTracker("UA-xxxxxxx-2");
pageTracker2._trackPageview();
} catch(err) {}</script>