I would recommend just putting a link to the file and letting the user download by clicking the link or even redirecting the user to that link. You could delete the file a day or so later or have the user confirm a successful download before deleting.

Else you will have to go to some kind of 'push' technology. 'Push' was a big thing a couple of years ago, but has pretty much died down (for several reasons including poor security). If you are interested you can check out this link about Push and Push Technologies on Netscape's site.