I can't give you specifics, but it would probably involve using Windows Task Scheduler and some batch file scripting.
For example, you could have Task Scheduler start Internet Explorer with that URL as an argument. The command line would look something like this:
iexplore
http://www.yoursite.com/filename.xls
(The only catch is that you'd have to tell Internet Explorer to always save files of that type)
Once the file is downloaded, you could run a second task that uses a BAT file to rename it.
Maybe that will spark some more ideas for you.