I have a product that has two weights options, 1lbs and 2lbs. Is it possible to set a Shopping Cart Price Rule condition for only the 2lbs item?
Here is a best way to apply Shopping Cart Price Rule condition.
New attribute that you made add to attribute set (Catalog > Attributes > Manage Attributes Sets)
When you add a product, have to use Configurable Product and select attribute set that you made.
under Shopping Cart Price rules.
setup condition whatever you want
Go to Actions and setup conditions as below
then It should be worked as you desired. I hope it helps you...