The long awaited MOM Availability Management Pack has now been re-released after problems were found with the original version (most notibly causing issues with the Exchange Management Pack and the Web Console).
However, I believe there may be an additional problem with the re-released Management Pack. This new problem is not damaging to an existing MOM installation and should not prevent the installation of the Management Pack. However, report generation may be affected.
I am currently tracing and troubleshooting this issue with the guys at Microsoft and will place an update here as soon as I have one.
Andy.