SQL Memory Usage

Hi All

I've been told that when dealing with 64bit SQL Servers with locked pages in memory enabled, using task manager to evaluate how much memory SQL Server is using is wrong.

What is a clear and concise way to retrieve SQL Server's memory usage on a server?

I came across the following script, can someone help me decipher what the columns actually mean?

select physical_memory_in_use_kb/(1024) as sql_physmem_inuse_mb,
locked_page_allocations_kb/(1024) as awe_memory_mb,
total_virtual_address_space_kb/(1024) as max_vas_mb,
virtual_address_space_committed_kb/(1024) as sql_committed_mb,
memory_utilization_percentage as working_set_percentage,
virtual_address_space_available_kb/(1024) as vas_available_mb,
process_physical_memory_low as is_there_external_pressure,
process_virtual_memory_low as is_there_vas_pressure
from sys.dm_os_process_memory

Thanks