so you're running 9i OEM and want to monitor 10g AS? I doubt you can do that. You can monitor the node where the 10G AS sits and write your own TCL scripts to monitor the AS via the 9i agent, but thats a lot of work. I may be wrong as I don't use AS.
You'll have to install the 9i agents if you've not already done so to do that.
Alternatively, set up 10G grid, then you can monitor them properly.
yes it is a windows thing, perhaps he missed the bit where you said LINUX ;-) Go to $ORACLE_HOME/bin. If there are a couple of files with 'dbsnmp*' then the agent is installed. Set the environment, issue agentctl start agent.
If not, then you need to install it. It will included on the software you used to install 9i in the first place.