How can I download previously purchased music to my current computer?
How can I download previously purchased music form an old computer to my new one?
Download Past Purchases
http://support.apple.com/kb/HT2519
OR...
If you still have Access to your Old Computers iTunes Library...
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.