Download and/or ship

Zen Cart 1.3.8a
Database Patch Level: 1.3.8
v1.3.8 [2009-05-27 00:33:43] (Fresh Installation)
v1.3.8 [2009-05-27 00:33:44] (Fresh Installation)

Had a good look around and can't find the answer or even a question relating to my wishes:

I have products that are:

1. downloadable
2. shippable
3. both of the above

First I used radio button for 1), 2) and 3) above but if I put download file in 3) then zen assumes its downloadable and doesn't ask for shipping address.

Second I tried only 1) and 2) as checkboxes...can select either one or both...great I thought but you can also select none of them and add to cart....

What I need is 2 checkboxes but at least one must be selected before add to cart..

Can this be done?

BTW still can't get my head around difference between download and virtual....got a simple explanation for it?

Has there been a solution for this issue - I need to have a few products to be either downloadable or they can be shipped.

Can someone point me in the right direction. Or am I forced to show the product twice - once as downloadable, the other as "add to cart"..???

Option Name: Delivery Method

Option Values:
Download
Sort Order: 10

Ship
Sort Order: 20

Select Delivery
Sort Order: 0

Attribute:
Option Name: Delivery Method
Option Value: Download
Filename: (fill in download filename)
Max Days: 7
Max Downloads: 5
Sort Order: 10

Option Name: Delivery Method
Option Value: Shipped
Weight: (whatever shipping weight is)
Sort Order: 20

Option Name: Delivery Method
Option Value: Select from below
Sort Order: 0
Default: Yes
Display Only: Yes

After all are added you can update sort order for the defaults or if manually entered you can skip that step ...