Currently Being ModeratedJun 14, 2013 8:13 AM (in response to djwillis250)
You will need to re-download your items (music, films and tv shows can't be re-downloaded in all countries), copy them from old computer, or from your backup of your downloads and add them via File > Add To Library. If they are still in the store then your apps and ibooks should show under the Purchased link under Quicklinks on the right-hand side of the iTunes store home page on your computer's iTunes, and, depending upon where you are then your purchased music, films and tv shows might show there as well.
What can be re-downloaded where : http://support.apple.com/kb/HT5085
Copying content between computers : http://support.apple.com/kb/HT4527