Administrators portal group not available

I was reading http://help.sap.com/saphelp_nw04/helpdata/en/a9/76bd3b57743b09e10000000a11402f/frameset.htm which recommends adding a second administrator for the portal. I logged into the portal as Administrator/admin, but I could not find any groups under 'User Administration > Groups' tab.

1) Why is the Administraors group not available? Is this not available in preview edition?

2) What other users are created as part of installaton? I was able to login to the portal as admin/admin too. How?

Thanks.