MySQL startup parameters

I notice that MySQL that OpManager installs is setup to use only 8megs of memory for Key buffers and it has nothing at all for Query cache. Is there a reason that OpManager is not using any memory for query cache?

Right now I am monitoring the following and I am looking at the optimal settings for MySQL and OpManager.

Routers - 144
Servers - 102
Switches - 4 (Cisco 6509's)
Firewalls - 4
PCs - 140

I am adding approx 30-40 routers a month and I have already changed the amount of memory OpManager can use from 200 to 1024.

Here are the specs for the Server running OpManager..

(2) 3.0ghz P4 xeon cpus
5 gigs of RAM
180 gigs of Raid5 drive space
Redhat 4.0 ES SMP version

It is running a load average 3.20, 3.21, 3.29

This server also runs deviceexpert but it is using almost no resources.

Any ideas?