Are you referring to network utilization or the server CPU utilization?
I'll assume CPU. In the Server Monitor, select Kernel, then All Threads. Find the ones that are running hot & heavy. You can also try "Businest Threads" which is likely a quicker way to find it. If you need more info on the Monitor tool, check here:
http://www.novell.com/documentation/nw6p/?page=/documentation/nw6p/utlrfenu/data/h74jxvbx.html