I have installed FMS v12.03 on a new iMac running ML, and even though FMS finds the Apache server and deploys ok, when you get to the overview screen of FMS, it states that IWP is not running due to a "communication error with the web server". I've tried to restart it and check the logs and it is generating a 701 error. Not sure what that means.
I think I read somewhere that they uninstalled FMS, deleted the IWP folder manually after uninstalling, then re-installed.
I did have some issues with the initial installation and it failed installation a number of times before I realized that the user name I assigned was FMServer and FMS creates a user named FMServer... consequently it failed.