This option is available for ShopSite Pro and Manager level stores. If you store is a Starter level store that would be why it doesn't exist. The options will display in the shopping cart only in Starter level stores.
You can determine the Version and product level of your store by Clicking on the ShopSite image in the upper left of any backoffice screen and then looking in the footer area between the 2 ShopSite logos. It will be something like
ShopSite® Pro 10 sp1, StoreID: jim Where the Pro would be Pro, Manager or Starter.
If your store is not a Starter level store and you aren't seeing the option under Product > Edit Product Layout then there is a problem. What fields so you see on that screen?