People have been often asking about supportability of different MOM components on x64 architecture. There is a lot of info on the web, but it’s a bit unsorted: http://support.microsoft.com/?kbid=917615, http://www.microsoft.com/technet/prodtechnol/mom/mom2005/Library/acb14db1-a3b3-4e65-9aae-c025e4718cfa.mspx?mfr=true

Here is my attempt at sorting it out:

• Agent: Only x86 and Itanium versions are available; you can monitor x64 computers with x86 agents which will run in WOW mode – the only (known to me) drawback, apart from agent performance, is that you might not be able to access some performance counters for applications that expose only x64 counters (for many you can enable this, e.g. SQL)
• Management Server: Only x86, meaning that on x64 servers you should install .net framework 1.1 x86 (required) and then install MOM management server software which will run in WOW mode
• OnePoint Database: Currently supported only on x86 and Itanium (with momcreatedb.exe tool from IA64 folder on MOM CD), meaning that on x64 servers you need to install x86 SQL and MOM DB will run in WOW mode. There is now a new update to install MOMDB on x64 SQL: http://support.microsoft.com/?id=921278
• SystemCenterReporting Database: Currently supported only on x86 – same procedure for x64 servers as for OnePoint DB
• Reporting front-end (SQL RS): : Currently supported only on x86 – same procedure for x64 servers as for OnePoint DB

Good news is that Ops Manager 2007 (though not in version Beta) when it RTM’s will fully support all components on x64 – databases, reporting, management servers and agents.