how to convert the following query to sql server 2005

hi

i have the following query in ms access and i want to convert it into sql server 2005 express edition

SELECT iif(Max(BNo) is null,1,Max(BNo)+1) AS BNo from ( 
SELECT iif(Max(Product.BNo) is null,0,Max(Product.BNo)) AS BNo FROM Product 
union all SELECT iif(Max(grndetail.BNo) is null,0,Max(grndetail.BNo)) AS BNo FROM grndetail 
UNION ALL SELECT iif(Max(srdetail.BNo) is null,0,Max(srdetail.BNo)) AS BNo FROM srdetail ) as t