Form/sub-form and query question

[Boozer]

First:
If I have form x which contains subform y and the subform contains texbox z, how do I point to that value from a module script. What I want to do is something like:
something in form(x).value = subform.textbox(z).value

Second:
I have a query which which sums the amount owed and amount paid of a table and groups by debtorID. What I want is the difference between the amount owed and the amount paid. Is it possible to get that from a single query?
ex.
Amount Owed Amount Paid
debtor1 $100 $5
debtor2 $1000 $1000
debtor1 $50 $0
debtor2 $10 $5

so the result of my query is:

Amount Owed Amount Paid
debtor1 $150 $5
debtor2 $1010 $1005

Data I want is Amount Owed - Amount Paid, like this:

Amount Owed
debtor1 $145
debtor2 $5

Thanks in advance for your help!