Hope This Helps.Just copy and paste.
SELECT dbo.custDetails.custID AS Expr1, dbo.custDetails.custName, dbo.custDetails.custLimit, dbo.custTransaction.custDueAmt
FROM dbo.custTransaction INNER JOIN
dbo.custDetails ON dbo.custTransaction.CustId = dbo.custDetails.custID
WHERE (custDetails.custLimit > dbo.custTransaction.custDueAmt)