EXEC sp_spaceused 'dbo.iboard'
---- もしくは下記のようにもできる ----
DECLARE @TableName varchar(100)
SET @TableName = 'iBoard'
SELECT B.rows
FROM INFORMATION_SCHEMA.TABLES A
JOIN sysindexes B
ON (object_id(@TableName)=B.id and B.indid < 2)
WHERE A.table_name = @TableName