First of all, to get the PCs to respond to pings, you need to go to the advanced settings under the firewall dialog in OneCare/Change Settings and in the Ports and Protocols list, you need to enable ICMPv4 Inbound.
For the Circle question, the manage your circle will appear if the PC is running 2.0. If all PCs are on 2.0 production (either upgraded from 1.6 or new install from http://onecare.live.com ) and not the beta code *and* activated with the same LiveID (Open One Care, Help/About to see your subscription ID) you will see the other PCs on your hub, but the option to manage the Circle will appear on the other PCs - you just can't actually manage the circle unless you make the PC a hub.
-steve