Actually this was the finished product:
SELECT Customer_ID, CustomerPO, Due, InvoiceDate,
IIf(([Due])>=Date(),Remaining,0) AS [0-29Days],
IIf(([Due]) <=Date()-1 AND [Due]>=Date()-29,Remaining,0) AS [30-59Days],
IIf(([Due]) <=Date()-30 AND [Due]>=Date()-59,Remaining,0) AS [60-89Days]...