Hi!
Yes, I tested this. It works ok, without IIS restart I see new phpinfo(). It is cool!
I installed PHP from zip too. I don't like installers too, because I don't know about their actions.

5.2, ISAPI + I install php5-isapi.reg from php folder, php.ini in Windows... Nothing special...
In article on php.net I read, that I can't change per-dir variables, only user-vars but I turn on register_globals and short tag for one of my clients ok (by default they are off in my php.ini), may be it is new feature in 5.2? I think, you should install 5.2 as ISAPI.
My default phpinfo() http://e-guu.ru/phpinfo.php, for example.