Heres one for YA

How do I create a virtual product, that can be downloaded by my customers, by clicking on a link in an email message?
And how do i have that email automatically sent to the customer, after they have completed a transaction on Paypal's website?
I have Paypal's Instant Payment Notification configured.
My customer will be re-directed from Paypal back to my site, to a conformation page that simply states that the customer must check there email at the address they provided at the Paypal site.
The message will contain a link for the customer to download the file.
For security I would like this download option to expire after the customer has received the file.

Uh - why not use the built in download functions in Zen Cart?

If the customer gets an email that takes them to their Order ... and their Order has the Link to the download right there ... what more are you trying to do?

This is already pretty automated ...

but how do i setup the email template?

o.k. ...
maybe i'm not explaining this right. I'll try again.
Here is the process i would like for my customers to go through.
They visit my site (already published)
the click on the "buy now" Paypal button(already installed)
complete the transaction (paypal will send data via IPN)
will be redirected to my wewbsite, to a page that simply reads
"Check your email"
When they read the email message, they should simply be able to click on a link to download a file.
I somewhat understand Products/attributes.
but have no idea how to setup the email message.
Ive seen a lot of requests for info on this subject, i cant believe there is not some documentation on this.
I'm basically selling a virtual product, but i cant find anything in attributes that describes "Virtual Product"
when considering your reply please keep in mind.
I'm an idiot, i dont understand this stuff.
a step by step how to would be awesome!

You're making it more complicated than it needs to be.

You'll need to take some time to understand the Attributes system in Zen Cart, and then use it to add the downloadable files to your Zen Cart products.

Then, after your customer purchases the downloadable product, they will come back to your site from Paypal and be automatically shown a link to download their item.... and the link will be valid for 5 days and 7 clicks ... or whatever you configure. They can also access the downloads from their My Account area in your store.

Adding Attributes:
http://www.zen-cart.com/forum/faq.php?faq=cats_and_prods#faq_add_attributes
and
http://www.zen-cart.com/wiki/index.php/Admin_-_Catalog_-_Attributes_Controller

Adding Downloads:
http://www.zen-cart.com/wiki/index.php/Downloads

Configuring downloadable products (discussion):
http://www.zen-cart.com/forum/showthread.php?t=35776&highlight=set+downloadable+products