When you get a web page like : from PHP running under IIS it is likely an issue with permissions. Some solutions include

• changing cmd.exe permission explicitly to be readable.
• Another was to remove the web server application user from one of the specific web groups that locks down the server. (Can't find the reference).
  

I get lots of "Warning: exec(): Unable to fork [cmd /c ...]" at the module's step in the installer for G2 (on the ImageMagick module) under Windows/IIS. Now what?

You need to give permissions for IIS to be able to read and execute the command interpreter ("cmd.exe"). Without it, Gallery won't be able to call external executables (like ImageMagick). Required steps:

1. Open a cmd-prompt with "Start", "Execute", then type "cmd.exe". Hit ENTER. 
2. At the prompt, type: 
C:\> cacls %COMSPEC% /E /G %COMPUTERNAME%\IUSR_%COMPUTERNAME%:R 

This adds the "read" permission to the IIS-user for the cmd.exe. Close the prompt and then try activating the imagemagick module again. More Info

e.g.
C:\>cacls %COMSPEC% /E /G %COMPUTERNAME%\IUSR_%COMPUTERNAME%:R
processed file: C:\WINDOWS\system32\cmd.exe

C:\>echo cacls %COMSPEC% /E /G %COMPUTERNAME%\IUSR_%COMPUTERNAME%:R
cacls C:\WINDOWS\system32\cmd.exe /E /G FRANC\IUSR_FRANC:R