dead-reckoning?

Anyone have a simple explanation for cubic-spine dead-reckoning??? I am designing a multi player 3d game using a high-up-over-the-shoulder cam. I don''t want to worry about 3 dimensions because the terran is mostly flat (the player can''t go underneath geometry). I read the gamedev.net article but i can''t seem to figure it out. Would somebody mind giving it a brief explanation of the theory/implementation the Cubic Splines in dead-reckoning? Any thing will help. Thanks A lot Kevin. Moo goes the cow