Hi,
I would create a query in your dataset that would return the item, year, month and total.
I would insert an extra field which would return the month number, so you can sort the months by number rather than name.
Then I would insert the month and total in the detail section of a table. The detail section normally has '=' symbol in the row header.
Add a group parent group for the Item and include a group header
Add a child group for the year and include a group header
For the drill down in the row groups right click on the detail group select properties and then select the visibility option. In this section select the option display can be toggled by this report item from the pick list choose the year.
Hope this helps