computer crash

I bought Microsoft Office 2003 student /teacher addition in march of 2006 last week a storm caused my computer to crash, I reformatted my hard drive and reinstalled the programs that came with my computer, However because I purchased the above mentioned program off the online transaction service, I do not have a CD copy for back up or reinstalling the software. I do have my product Key code and my transaction #. How can I get a copy of the soft ware once again without having to repurchase again?