Then I looked at your relationships.
You need to focus on your tables--they are incorrectly set up. You should not have seperate tables (or fields) for debits and credits. They should all go into the same table, and their values should go into the same fields. For example:
TableTransactions
TransDate, TransCustomer, TransAmount
1/2/2008, 17, 90
2/3/2009, 18, 11
1/4/2010, 17, -90
The first 2 transactions are credits (positive), the last transaction is a debit (negative). Now, if I want to add them all up to get a balance its super easy because I just have to use the SUM function on my TransAmount field.
Looking closer at your tables, I don't see the need for 4 seperate tables for transactions. My guess is that all those tables' data should go into 1 table.
Focus on that, then worry about forms.