Contributed By: Bill Hodghead [MSFT]
That is one upgrade path, however it is not the only one for 2000 to 2005.

The MOM 2005 agents can talk to the MOM 2000 servers. The main purpose for this is if you have multi-homed agents and you can't upgrade all your management groups at once. You can upgrade all of one group but leave the other. You will need to add the MOM Transition MP to the MOM 2000 server so that you can continue to monitor MOM events on the agents - the agent service name has changed so the old MOM MP won't work on the new agents.

A third upgrade path is to create a new MOM 2005 server and multi-home the agents you want to migrate to it (instead of upgrading in place as above). This can be good if you are upgrading hardware at the same time.