Microsoft Visual Studio 2005 Reporting Services

Hi everyone! I had a question about the query side of the reporting services...
I'm tying to develop a comparison between the most recent entry and the second most recent entry in our database... the first part would go something like this...

SELECT TOP (1) Invoice.InvoiceID
FROM Invoice INNER JOIN
WorkOrder AS InnerWorkOrder ON Invoice.WorkOrderID = InnerWorkOrder.WorkOrderID
WHERE (InnerWorkOrder.AffiliateID = Affiliate.AffiliateID) AND

//**
and this is where I need the comparison...

(DATEDIFF(m, "SECOND FROM TOP ORDER", "FIRST ORDER ON LIST") <= 13)

**//

Anyone who can help me with this I would greatly appreciate it... thank you in advance