Do you mean a 3rd person, as in you look at the character with the sword, or 1st person where you look from the character's eyes?
For 3rd person, you should already have a person model, and if ther model is good enough it will have arm and hand limbs. If it has a hand limb you can attach the sword to that, and then rotate the arm and hand about to swing the sword. If the character doesn't have a hand or arm limb, then you have to attach the sword to the body and offset it to the approximate position of the hand. In this case, you probably wouldn't be able to do anything except rotate the sword.
In a 1st person view, you can lock the sword onto the screen as you would with a gun, and then rotate and reposition it relative to the camera to acheive the swing.
Once I was but the learner,
now, I am the Master.
