Dynatrace AJAX Edition is what you want, although it can take a while to use.
Dynatrace has some good video tutorials / conversations online.
It's free too
I know IE9 has a script profiler built into the dev tools (press F12 to access). I know IE8 has the same tools, but not sure if it has a profiler. If it doesn't have a profiler, you can always use IE9, put in IE8 browser mode.