Prior to Cataclysm, tanking was possible in any of the 3 talent trees; Frost being traditional-style and unholy for magic bosses. Blood spec is the death knight tanking spec, while Frost spec and Unholy spec are the DPS specs. Death knights are able to dual wield and use two-handed weapons, however, this is only advised for the properly spec'ed Frost death knights. It is advised to put your higher DPS weapon in the main hand to maximize damage output when possible. Death knight skills scale off Attack Power, not Spell Power.