If anyone struggles getting iTunes to complete the download, consider downloading the file directly to your desktop from our thread here - http://www.ipadforums.net/ipad-hacking/24939-official-apple-ios-firmware-download-links-ipad.html
Then, once it is downloaded, shift-click (windows) or option-click (OSX) the restore button in iTunes and it will let you select the file you just downloaded.
iTunes can time-out, particularly when the whole world is trying to install IOS5 at once!
Thank you! IOS 5 has finally installed and the iPad is syncing right now.