I'm running PHP under IIS for development, works like a charm. Everything i write also works on Linux & Apache, so you don't have to worry about that too much. Even file managers and stuff like that.
I run the isapi module and don't have problems at all. It's fast and stable, crashed only a few times in the last 2 years (because of some reall bad looping).
I don't have a pc running on Apache myself at the moment, so i can't tell you for 100% that its as fast as running it on Apache. But i don't think it's slow at all, it's the opposite.
This is how i set it up (i've used these settings on serveral pc's with IIS):
-> run -> inetmgr
// To run PHP on 1 website only
-> open "Defauilt Web Site" (if you haven't renamed it)
// To run PHP on multiple sites that IIS hosts
-> openwebsites (second open after openening Internet Information Services at the left)
-> properties
-> ISAPI filers
-> Add
-> Filtername PHP, Executable (locate php4isapi.dll)
-> Then to Home Directory
-> Configuration
-> Add
-> Executable: php4isapi.dll
-> Extension, whatever you'd like to use, .php, .phhtml, etc
-> properties -> documents, there you can set the default documents, index.php perhaps?
Restart IIS or restart win and it should be working. Make sure your php.ini settings are correct, i needed different values for some options on different pc's. I haven't got a clue why :S
i hope its usefull, good luck