Jack's right, the pine you found at HD is not for decks. You can use it for eaves - a protected place. In a previous answer I mentioned CEDAR t&g. Treated pine will be good too. There are other types that will be fine for a deck, all of which are rated for outdoor use.

You need to go to lumber outlets, AKA lumberyards. Look them up at the phone book or google. Places like 84 LUMBER, STOCK LUMBER or similar.