From what little you have posted about your mdb, it sounds like you might have a table for each year. This would be a bad design; all years should be in one table. Also, since the balance can be calculated at any time, you shouldn't store the balance in a table.
To answer your question, in a query, add two columns. In the new columns add:
Code:
Field: TheMonth: Month(DueDate) TheYear:Year(DueDate)
Criteria: 1 2011
If you wanted all entries for Jan, the criteria for TheMonth column would be 1 and the criteria for TheYear would be 2011.