download microsoft office after hard drive replaced

The hard drive in my Macbook pro crashed and I lost everything, including my microsoft office program. I don't have the disks, but have one of the available keys that came in the 3-pack. Is there somewhere I can download the full office program? Ideally, I'd rather not use this final key, but somehow recover the old key since everything was lost due to the crash. Sound advice is appreciated. Thanks.