i click on the Install button within the store, it appears in my Launchpad, but just says downloading. The progress bar doesn't change and stays at 0 for the percentage. I left the computer for a little while hoping it would download, and when i came back, Xcode disappeared from Launchpad altogether,
"If you tried installing Xcode from the App Store and have experienced some hangs, there is a workaround that should get the package installed. Go to the "Install Xcode" application that you downloaded from the App Store, right-click it, and choose "Show Package Contents." Then go to the "Resources" folder and you should see a file called "Xcode and iOS SDK.mpkg." Open this file, and the OS X installer will run to install Xcode, but this time it hopefully should install without any hangs."
From here > http://reviews.cnet.com/8301-13727_7-20052216-263.html#ixzz1hOPPy2k4