If the swing is all one piece, just parent the figure's Hip to the swing.  If the
swing is built in separate pieces (chains and seat) parent the Hip to the seat.
After that, don't worry about trying to attach the hands; simply adjust the
figure so the hands happen to be on the chains at each frame.

This little animation was done that way.....

http://ockhamsbungalow.com/Movies/Swing.swf

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