Will this module calculate a shipping quote if my product has a weight of zero?
Yes, by default the module will quote for a shipping weight of one pound should it find that the overall order weight is zero.
If you want to offer free shipping for a certain shipping level then you can set an overall shipping markdown of 100% for that level. You can also set a specific shipping price on a product level.
For example, you could offer free Priority shipping on a Toshiba L670 laptop or $25 Ground shipping on an Oak Computer Desk.