In SQL2008 you probably want to use sys.dm_exec_sessions and identify sessions that have been idle for the last 30 minutes:

DECLARE @idle_timeout int = 30; -- minutes

SELECT session_id

,status

,login_time

,host_name

,program_name

,host_process_id

,original_login_name

FROM sys.dm_exec_sessions

WHERE status = 'sleeping'

AND last_request_end_time < DATEADD(minute, -1 * @idle_timeout, GETDATE())

AND is_user_process = 1