Got a new computer and want to move your entire iTunes library? With iTunes 8 there is a backup feature that will archive your entire library to CD or DVD, including ratings and playcounts, which can be moved to another computer. If you are interested in moving your library using this method click, here.
If you do not have access to a CD or DVD burner then there is another option if you own an iPod. Because your iPod contains a high-capacity drive, you can use it to move all your music from your old computer to the new one (this document does not apply to iPod touch).
Note: While you can use the Transfer Purchases from iPod option under the File menu to copy iTunes Store purchases from the iPod to another computer, you can't transfer songs from other sources from the iPod library to iTunes, so you'll need to follow the steps below to use iPod as a hard disk to transfer music files from one computer to another. This process will require the use of iTunes 7 or later on all computers. Any computers running iTunes 6 or earlier will need to be updated to follow these steps. Download the latest version of iTunes here. Once you have the files transferred, you'll need to authorize any iTunes Store content. If you won't be using your old computer, you'll want to deauthorize it.
Important: Windows operating systems don't recognize Mac OS-formatted disks (HFS or HFS Plus formats), so you can't use a Mac-formatted iPod to move your music to a Windows PC. See "iPod: How to determine iPod's hard disk format" if you're not sure what format your iPod is.
http://support.apple.com/kb/HT1329