Find what script is being run by specific SPID number

DECLARE @sqltext VARBINARY(128)
SELECT @sqltext = sql_handle
FROM sys.sysprocesses
WHERE spid = 53
SELECT TEXT
FROM sys.dm_exec_sql_text(@sqltext)
GO

SQl Server "How is My Memory Being used" Performance Counters"

Reference: http://www.quest.com/backstage/images/promotions/SQLServer-Perfmonance-Poster.pdf