This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
First things first, the reason why your ball isn't at the center of your cursor is because your mouse listeners are registered to a JFrame object, a JFrame is the whole window frame so the 0,0 coords are actually at the top left corner of the frame (above the java icon). Add the mouse listeners to the Skwer object instead
or make a JPanel inside the JFrame and register the listeners to it instead