i have a {Leaden Myr} and I was wondering I just now summon it can I tap it for the black mana or does it need haste?
All creatures are affected by summoning sickness, unless they have Haste. Artifact creatures are no different from nonartifact creatures when in regards to summoning sickness.
However, only tapping activated abilites cannot be done the same turn the creature enters the battlefield under your control since summoning sickness basically prevents a creature from tapping.
Also, this feels more like it should be under the rules section of this forum.