Decrease speed script

How do I decrease or increase speed on the animations? for example I just want a text to move from right to left but as its get close to the left to start slowing down until it gets to wher I want it, I hope you know what I mean, If not this is a site that uses that when text goes up or down or the buttons .

http://www.nenajaye.com

Thanx please Im new to this so please explain how to modify the script :thumb2: