scom doesn't detect exchange 2007 servers

this is by design in scom 2007 r2. a few simple steps will get you there though.

verify discovery helpers
-don't scope your views and click on "discovered inventory" in the monitoring pane
-right-click and click "choose target type"
-type "Exchange 2007 Discovery Helper" in the look for field
-exchange 2007 servers should appear w/ "not monitored" status

enable the discoveries (see note2 and image below for more info)- http://blogs.technet.com/momteam/archive/2010/02/23/exchange-2007-management-packs-do-not-automatically-monitor-exchange-servers.aspx

note1: discoveries only run every 24 hours (86400 seconds), so i'd recommend changing that override as well when enabling the discovery for each exchange 2007 role. change it something like 120 or 180 seconds, wait for the discovery and verify in the monitoring pane, then remember to change it back to the default (86400 seconds).

note2: hub transport and client-access are easy to find in the list of object discoveries. mailbox role is under the rule named "Exchange 2007 Standalone CCR Node Discovery". everything else is pretty self-explanatory.