"In a NUMA-enabled system, this value can be incorrect or negative. However, the overall
value in the Memory Manager section is a correct value."
I received this output from an customer today. When I investigated it I found a known issue that was not corrected in SQL Server 2005 that allows a calculation to rollover a LONG value but prints out a LONGLONG value. So depending on the calculation it may a negative or an unexpected large value in some instances.
I did find a source check-in for SQL Server 2008 that corrects the behavior.
You can look at the 'Memory Manager' AWE Allocated to get the correct AWE Allocated value instead.