Hi Low Rider,
See if this helps (http://msdn.microsoft.com/en-us/library/ms176013(v=sql.105).aspx):
SELECT TOP 10 login_name, SUM(cpu_time)
FROM sys.dm_exec_sessions
WHERE session_id > 50
GROUP BY login_name
ORDER BY SUM(cpu_time) DESC
Basically will give you the logins with most CPU time usage, but only for the current sessions.