Para expandir, o outro (também correto) responde um pouco mais, de windows.php.net :
Which version (of PHP for Windows) do I choose?
If you are using PHP with Apache 1 or Apache2 from apache.org you need to use the VC6 versions of PHP.
If you are using PHP with IIS you should use the VC9 versions of PHP.
VC6 Versions are compiled with the legacy Visual Studio 6 compiler.
VC9 Versions are compiled with the Visual Studio 2008 compiler and have improvements in performance and stability. The VC9 versions require you to have the Microsoft 2008 C++ Runtime (x86) or the Microsoft 2008 C++ Runtime (x64) installed.
Do NOT use VC9 version with apache.org binaries.
Espero que isso ajude.