I was attempting to install Microsoft Operations Manager 2005 on my laptop a week or so ago, and struggling to work out why the MOM installed kept saying that the pre-requisites for installing MOM weren't up to scratch. Specificially, it was complaining that SQL Server 2000 SP3 or later was not installed. I knew it was, in fact I had SP4 installed. Fortunately, the answer was already out on the Internet. You need to "tweak" the registry temporarily during the installation to make MOM think that SQL 2000 SP3 is installed, and then change it back again afterwards. Annoying.
Here's Russ Kaufmann's explanation of the steps you need to follow.
If it is an option, upgrade SQL Server SP3a to SP4 after MOM 2005 is installed. A bit more work (start with SQL Server SP3a first) but could not find a solution earlier in my case unfortunately (1 day actually :-).
So hot off the heals of getting MOM 2005 installed with SQL 2004 SP4 , I find out that SP1 for MOM is...
I just came across this article on the MOM Product Team blog and thought you would be interested as it explains how to bypass the prerequisite checker.
see http://blogs.technet.com/momteam/archive/2005/08/01/408517.aspx for details.
You will also note that I included the KB article on another method to achieve the same goal in my blog entry.
MOM SP1 is supposed to fix this issue.