John Mertic has a quick note on his blog about the latest release candidate for the Windows PHP installer (PHP5.2.0RC3) and some issues they've been having.

Rebuilt the installer for 5.2.0RC3. Edin was having problems building it so I'm going to do it and upload it; hopefully we can resolve the issue.

It's also noted that if you see issues with using the installer, try removing the previous PHP installation before running it again.