After installing Ops Mgr 2007 RTM I decided to tackle an ACS installation. The ACS database and application install went smoothly, but the ACS service would fail to start explaining that "Access is Denied".
I recalled reading a post by TheTallest in the ACS beta newsgroup that spoke of a similar issue. The 'solution' was to rename the AcsConfig.xml within the C:\WINDOWS\system32\Security\AdtServer directory and create a new file entitled AcsConfig.xml. Simply copy the contents of the old AcsConfig.xml to the file you just created with the same name and viola! - the service starts without issue.
Hopefully, Microsoft will speak up/fix the issue in the coming weeks.