Hiya Max,
You are going to need something like a secure download script. One that I use all the time in conjunction with EE is Linklok URL. I had to get the developers of the script to modify it ever so slightly so that the PHP file would work as an include from within EE templates but I literally have never found a better script than this one to use with EE and I must have tried over 50 of them when I was first looking for one. There are some free scripts out there but most of them have an admin area only where you have to input the file to download and then it creates the secure link for you which means that this wouldn’t be as easy to use with the Simple Commerce Module. Linklok has a link generation form but you don’t have to use this if you include the Linklok PHP file in an EE template.
The way I use it is in conjunction with a great plugin that my learned Friend Andy (aka ExpressionEngineer) created. I’m sure if you asked him nicely he would let you have a copy of it although with the amount of people I have put in touch with him about this he really should start charging for it!! Andy if you are listening to this or come across it then I want some commission mate!! 😉
So basically what you will have is a custom field that just holds the name of the file ie my-file-to-download.zip which is stored with each entry that you are using with the Simple Commerce Module.
Once a person has successfully purchased an item using the Simple Commerce Module they can immediately go to a http://www.mysite.com/downloads/ area on your site and there will be a weblog tag surrounded by Andy’s plugin tag which basically spits out all weblog entries that you have paid for. In turn you then use Linklok which is a php file included in your EE template to create the secure links.
May all sound a little convoluted but trust me it does work brilliantly as I have done this on a site which is selling many mp3 files and it works absolutely flawlessly. We keep on getting repeat orders because everyone who has purchased through the site has praised just how easy it was for them to use.
Hope some of that throws some ideas your way?
Best wishes,
Mark