With the forthcoming August release of the Availability MP that will make it the third release. There may be another update later this year too which will support Windows 2000 domain controllers (more on this when I know more).
With that said, and with MOM installations moving between administrators, it can be hard to tell which version of the Availability MP is already installed when taking over administration of an exisiting implementation. So here's the low down:
A brief history lesson ;)
The Availability MP was first released in September 2005. This version had an AKM version 05.0.3000.0000. Performing the SQL query SELECT * FROM MRAS_MRASInstallVersion again the SystemCenterReporting database would return TableVersion 1.0 and ProcVersion 1.5.
The Availability MP was re-released November 2005. The AKM version is 05.0.4000.0000 and the TableVersion 1.0, ProcVersion 1.5. Hence the management pack akm was revisioned, the SQL Server components remained the same.
The forthcoming Availability MP (August 2006 release) has an AKM version 05.0.5000.0000. The TableVersion remains 1.0, but the ProcVersion has been rev'ed to 1.8. Hence the management pack akm was revisioned and the back-end stored procedures were revisioned.
Hopefully this should prevent any confusion over what you currently have installed :)