1. Create a Gift query to group together the pledges that have an outstanding balance

     a.  Create a Constituent query
     b.  Filter on Summary Information, Summary for Gift, Pledge Balance
           Note: For a summary amount within a specific date range, fund, etc., use the Filter tab on the Edit Field Criteria window

Or
 
     a.  Create a Gift query
     b.  Filter on Gift Information, Pledge Balance

2. Create a Gift export for this query
3. Export pledge balance