iPod Problem transferring purchased iTunes to my iPod

Hi Hi Everyone,

My old Powerbook had a fried logic board, so I claimed on my insurance and luckily got a new MacBook Pro. I transfered all my music, photo's and files to the new MacBook Pro which went OK. Problem is when I plug my iPod in I get this message "Some of the items in the iTunes library were not copied to the iPod "Mark Mitchell's iPod" because you are not authorized to play them on this computer. I don't understand how I can play them in my iTunes library but not on my iPod.
Do I have to buy all these tracks again ????

Cheers
Mark

How do I de-authorize and re-authorise my computer ???

Cheers
Mark

All sorted, working fine now. Many thanks for your help.

Cheers
Mark