We required a similar setup where the web site is hosted remotely (this is where the html pages reside (PHP/XML). The PHP / IIS is on a local box as well as Filemaker Server 9 and Web Publishing engine (MS XP sp 2 - can't use SP 3 because it breaks SSO). Alternatively, you could install Filemaker Server 9 on one box and the PHP/IIS and Web Publishing engine on a separagte box to obtain additional processing speed. We have everything running with SSL including between clients and server.
I hope this answers your questions.