In my very quick research, it looks like aWeber does not have any sort of API that would allow you to send special commands like this. (passing a unique URL and triggering the email)

One very quick solution (though not integrated with aWeber) is this lovely little site from a fellow Warrior member: Sell eBooks, Files, Downloads, Digital Products with Paypal - UPLOADnSELL.com

-Ryan

Why does it have to be aWeber?

Just use regular PHP Send function to give users temp download link.

If you're experience programmer, you can do following, UPON successful payment

1 you already have yourdomain.com/downoad/ directory

now automatically script would:

2 copy original file (from password protected directory) to download directory with UNIQUE random ID attached to the name (i.e. download/1354324322341product.exe)
3 create same unique download page "1354324322341get.html" with link to 1354324322341product.exe file in same directory (yourdomain.com/download/).
4 send email with link to http://www.yourdomain.com/download/1...322341get.html that has link to your 1354324322341product.exe copy of original file (you could send link to actual file but it's cleaner and nicer way to send link to a page that has download link)
5 setup cron job to remove files older than 48 hours in download/ directory except for blank index.htm file

Rinse wash repeat for every purchase.

Well wait - there is no reason you can't do this with awebers custom fields/tokens (whatever they are called).

Add a custom field and put their session id in.

At same time put session id in database with time stamp.

Use token in first message message to include a page with session.

Have download page 'expire' if it's been to long.

I use it to change out affiliate links when someone opts into my sites so I know they get credit instead of me getting credit so tokens are certainly possible with aweber. And there isn't a reason you couldn't use it how I outlined above if you have just a wee bit of php skill (nothing complicated there).