I was downloading PHP recently and found that there are a few options available. Thought I might help you guys sift through a bit quicker with this:
VC9 was compiled with Visual C++ version 9. VC6 is the legacy compiler of Visual Studio 6 (4 versions behind, soon to be 5.) The VC9 binaries have a lot of improvements in performance and stability. But you can't use the VC9 binaries with Apache, so you must use VC6 in that case.