option name manager:
option name = download
option type = radio button
Option Value manager:
choose the "download" option name from the dropdown and then type "zip file" in the option value text box, then hit insert
Attributes controller:
Select category, then select product. Under adding new attribute select the correct option name and value from the drop downs. Then in the attributes flag section change "Default Attribute to be Marked Selected:" to yes and leave the others alone. Next step is to input the filename of the download and set the expiry days and maximum download count. (Note: you should have already uploaded the file to the downloads directory.) Hit insert.
Then go to the downloads manager if the file is list there with the little green circle under filename then everything should work.