1. Create a new constituent query
2. Filter on Gift Date between X - Y
3. Add any other gift criteria as needed
4. Sort the query by Gift Amount (Desc)
If you only need to pull a specific number of 'top donors', select Tools, Query Options... and make the query format Static. On the Record Processing tab, mark Apply Output Limits. Select 'Limit to top rows' and enter the number of constituents to save with the query. Click OK and save the query.