If you purchased a download it was done through asknet. You can go to their customer service and fill a request for another copy. I don't know if they charge for this or not.
http://asknet-en.custhelp.com/cgi-bi...mwmcF9wYWdlPTE*
You should back up all downloaded software to CD before you install it then do the install from the CD to make sure you have a good copy on your backup CD. take a marker and write the SN/key on the CD along with the name of the software. Do this for EVERY piece of software you download (even free ones) and you will not get stuck like this in the future.