Plugin Item Entity Handling

Hi, I was wondering how to track a specific item in bukkit like in the speedball plugin found here: http://dev.bukkit.org/bukkit-plugins/speedball/. Basically it lets you play soccer with a slimeball and whenever you get within about 3 blocks of the item it moves forward. I wanted to know how to put an id on that item(in this case a slimeball) and track it's location.