as davey said, just install the agent on the host and it (should) discover all the targets avaliable. I find pulling the agents from the OEM the simplest method, just give the agentdownload scripts the OEM details and it'll do the rest.
In 9i i used to add database to the tree which connects to the remote host and upon contacting the agent it refreshes all the databases and puts under my db tree in 9i OEM window.
I have two servers, A has oracle 10g oem database and a dev database. In this server I have the OEM set up and it picks up the dev database to EM window using the 10g agent. Now in this 10g EM window i want all my production 9i db's which runs on remote server B. I have the agent running on server B and the service names are listed in 10g tnsnames file.
Disclaimer: Advice is provided to the best of my knowledge but no implicit or explicit warranties are provided. Since the advisor explicitly encourages testing any and all suggestions on a test non-production environment advisor should not held liable or responsible for any actions taken based on the given advice.
When i log in to OEM it opens along with the database, there is no separate common windows for EM. When i use the "http:\\local_host:1381\em\console" goes to the database login screen with username/password and connect as.
I do not see even i login to the database the path you have given. I fear I am not in right track. Is that some thing I am missing?