Need formula to give me depreciaion for all time up to but not including current year.

I am looking for a formula that will give me straight line depreciation for all time up to the current year. Then separately, the depreciation for the current year.

So for example:
I bought a product for 10,000.00 on 8/1/07 with it's useful life being 20 years. I need to know the depreciation between 8/1/07 and 12/31/11 as that is the lat full year (that total can be added up). Then the depreciation for the current year, so 1/1/12-12/31/12.

I am really stuck on this one and would appreciate any help.