Help with formula field

I have a formula field in my report called "net due", as follows:

{vwTranJrnlChgs.Fee} - Sum ({vwTranJrnlPmts.Amount}, {vwTranJrnlChgs.Voucher_Number})

How can I change this formula so that this field will only show up in the report if the result is greater than 0.00?

(I only want to include outstanding balances, nothing else)

I will eventually want a grand total of this field as well (showing total amount of outstanding balances).

Thanks.