The Web Platform Installer (WPI) is really nice when it works. But when it doesn't, it's a battle to the death to get things to work. Case in point: I was trying to install php on my Windows 2008 Server through WPI, but it would go on forever during the FastCGI install step. I looked at logs and the Event Viewer, and searched google. A lot of people reported a similar problem, but there was no definitive recipe to get past the problem.
In the end, I just clicked on the link for FastCGI in the installation details window of WPI, and installed that piece manually. It went through without a hitch. After a restart (which the FastCGI installer required), I installed php from WPI, and it installed the 4 remaining pieces without a hitch, and it did so quickly. So just a note that if WPI starts acting up, just install the problematic piece manually and then let WPI continue.