If you still have Access to the Old computer you used to Sync to...
and to have EVERYTHING as it is Now...
From your OLD computer...
Copy your ENTIRE iTunes FOLDER to an External Drive... and then from the External Drive to your New Computer..
Full Details Here > http://support.apple.com/kb/HT1751
An Added Bonus is that you will have a Backup of iTunes.
If not...
See these 2 Links...
Syncing to a New Computer...
https://discussions.apple.com/docs/DOC-3141
Recovering your iTunes library from your iPod or iOS device
https://discussions.apple.com/docs/DOC-3991