If your friend is running a web site for his small business, then I whole-heartedly recommend Apache. It'll save him hundreds of dollars, and, potentially, a lot of security problems. I don't know about performance differences between Apache and IIS (I'm sure you can find dozens of contradictory benchmarks by Googling it), but specifically concerning which runs PHP better, I doubt you'll find much difference. Neither is "optimized" for PHP in any way, and both of them make use of PHP in pretty much the same way. Any performance difference will be related to all parts of the site, not just PHP files.
And if you're looking for a LAMP-like product for Windows, try WinLAMP ("WinLAMP Is Not LAMP"). I haven't tried it, but it should get the job done, though I assure you installing Apache, PHP, and MySQL manually one at a time isn't terribly difficult.