SQL 2008...

declare @a as bigint, @b-2 as bigint

select @a=sum(cntr_value)

from sys.dm_os_performance_counters

where object_name = 'SQLServer:Resource Pool Stats' and cntr_type = 537003264

select distinct @b-2=cntr_value

from sys.dm_os_performance_counters

where object_name = 'SQLServer:Resource Pool Stats' and cntr_type = 1073939712

select cast(@a as float) / cast(@b as float)*100 as [cpu]

go