If you must email the user the download:
Use ecommerce to setup the products as digitial downloads. give them a price of 0.00 and use the "Free" payment method type. Create an account for the user when they fill out the checkout form. Then use appropriate layout/styling/scripting to make sure the whole system does not look and feel like an actual store. May require some finesse, but should not be to difficult.
Much easier though to just create literature items and put them behind a secure zone. Let the user fill out the form which will also subscribe them to the zone, and then they goto a secure page on the site where they can click the download link.
The email part is what makes this complicated.