Can I brine my turkey with regular salt, or must it be kosher?

DB is correct as far as being able to use regular salt (you can substitute kosher salt for regular when the salt is dissolving), and also that it would take less regular salt than kosher salt - however when substituting kosher salt for regular salt - if you were using 1 teaspoon you would add 1/4 to 1/2 more of the kosher salt. So if you're figuring in cups - you would use 1 1/2 cups of regular as opposed to 2 cups of kosher. This isn't because it's saltier, but because regular salt is fine and more of it fits in a cup than kosher salt.