Some background first.

I'm a motorsport photographer and I sell photos through my shop. I offer images on a disc or as download. To this point I'm selling everything the same way and then e-mailing the customer a link later with the download details. I want to streamline this and use the download option in the shop.

Ok so where is the problem you ask. Well lets say I shoot a rally. There could be 100 cars and each car will be a separate item as a drop down menu in a particular product.

Again I can hear a few say where is the problem. The issue is I don't want to have 2 drop down menus with complete listings which is the only way I can achieve this now. ie
a download drop down with 1, 2, 3, 4, 5, etc
a disc drop down with 1, 2, 3, 4, 5, etc

What I would like is a drop down with car numbers and a drop down with disc, download. ie

car: 1, 2, 3, 4, 5, etc
type: disc, download

If you select disc and 2 you will purchase a disc with car number 2 on it and will be directed to the checkout with shipping included.

If you select download and 2 you will purchase a download of a zip file of car number 2.

Anyway the idea is how do I go about this?

As said I don't fancy having 2 complete drop down lists as it might lead to confusion. The type select and then a car list would be much simpler.