The only reason I keep using my aging PC is because it has my entire music collection on it. Meanwhile, my MacBook has been collecting dust. So I finally got around to transferring my collection this weekend. This is how I did it:

1. Sync your entire music library and playlists to an iPod of sufficient capacity. This is known as the auto-sync feature that basically mirrors your library onto your iPod.
2. Download iPodRip and install it on your Mac
3. Connect your iPod to your Mac. Let iTunes start up and recognize it, but just cancel when it asks you if you want to erase your iPod. You clearly don’t want to do that. Or do you?
4. Start iPodRip. It will recognize your iPod collection.
5. Click “Recover iPod”. Use the default options. “Recover iPod” is a two-part process. The first part transfers the audio files from your iPod to a temp directory on your Mac. The second part reads the meta data from your iPod and imports the songs into iTunes. This second part is why you need to leave iTunes running during this process.

iPodRip may crash during this process. That’s ok. Just eject your iPod from iTunes, close down iPodRip and iTunes, and then reconnect your iPod. Basically you’re going to repeat steps 3 - 5. iPodRip will start from where it left off.
Once you successfully import your library, you can disconnect your iPod and reconnect to your Mac. After you reconnect, you can now perform an “erase and sync”. It’ll be like you were never had your library on Windows to begin with.