There is a simple and official method to transfer an iTunes library from one machine to another (either PC or Mac). To use this, go to the File Menu, select Library, then choose Back up to disc. You'll then be able to back up your library to one or (if needed) more CDs or DVDs. You can then simply insert the first disc into your new machine and click Restore on the window which appears.
The downside of this is that large collections can take some time to burn to disc and will use several discs – 20 or so if you have the largest iPod filled to capacity.
Another option is to use the iPod itself to move the tracks. Unfortunately you can't simply move the music from your iPod to the new computer as Apple blocks this to prevent piracy (people might use this to transfer music to a friend's machine). Instead you have to use your iPod as an external hard drive, as detailed on Apple's site:
If you are using a webmail service such as Gmail or Hotmail, you don't need to do anything other than make sure you know your log-in details. But if you are using a program on your computer such as Outlook, you'll need to transfer the files.
How to do this and how well it works will depend on the program you are using, but the general principle is to use Mozilla's e-mail program Thunderbird as a middle step. Once you have installed and opened Thunderbird you'll need to use the Import Mail tool. Thunderbird will then create a single file containing all your e-mails.
To find this, go to Account Settings, then choose Local Folders and finally Message Storage, which will list the location of the file. You then need to find this file in Windows Explorer and rename it as Inbox.mbox, clicking Yes when asked if you want to change the file extension. Now copy this file across to your Mac.
When you run Mac Mail for the first time and set up an account, click Import mailboxes at the end of the set-up process. Choose the Other option, find the Inbox.mbox file and click on Import. This will create a folder called Import, from which you can select all your messages and move them to Mac Mail's inbox,
Transferring an address book works on much the same principle. When asked to choose a format for your exported in Thunderbird, choose LDIF. After copying the file to your Mac, you can import it using File > Import > LDIF.