If you didn't make a back-up of your music/movie purchases to restore from (as you are advised to do) then I'm sorry to say that the policy on lost purchases is that you have to pay to download them again:
"Products may only be downloaded once; after being downloaded, they cannot be replaced if lost for any reason. Once a Product is purchased or rented (as applicable) and you receive the Product, it is your responsibility not to lose, destroy, or damage the Product, and Apple shall be without liability to you in the event of any loss, destruction, or damage"
iTunes Store: Purchased content can be downloaded only once
If you have an iPod that still has any of your purchases on it you'll find details in this article on how to transfer them to the computer:
Copying iTunes Store purchases from your iPod or iPhone to a computer
Purchased applications can be downloaded over again, see this article for details:
How to redownload purchased applications from the App Store
Failing this, you could try contacting iTunes Store Customer Service and you might be able to persuade them to sanction a second free download. There have been occasional reports in the iTunes forum of this happening, however just be aware that they are not under any obligation to do so. If you click on this link it'll take you to the support/contact page:
Customer Service - iTunes Store Support
You might also want to check out these pages for future reference, you don't need a CD drive in particular to back things up, there are other methods:
Back up your iTunes library by copying to an external hard drive
iLounge - The Complete Guide to Backing Up your iTunes Library
