Switch iPod Classic from PC to Mac

You can copy what you have on the iPod to the Mac first and then restore it (which will reformat the iPod for Mac). If you have any iTunes Music Store purchases the transfer of purchased content from the iPod to authorised computers was introduced with iTunes 7. You'll find details in this article: Copying iTunes Store purchases from your iPod to a computer

The transfer of content from other sources such as songs imported from CD is designed by default to be one way from iTunes to iPod. However there are a number of third party utilities that you can use to retrieve music files and playlists from your iPod. I use Senuti but have a look at the web pages and documentation for the others too, you'll find that they have varying degrees of functionality and some will transfer movies, videos, photos and games as well. This is just a small selection of what's available, you can read reviews of some of them here: Wired News - Rescue Your Stranded Tunes

Senuti Mac Only
PodView Mac Only
PodWorks Mac Only
iPodDisk PPC Mac Only (experimental version available for Intel Macs)
iRepo Mac & Windows
iPodRip Mac & Windows
YamiPod Mac & Windows
Music Rescue Mac & Windows
iPodCopy Mac & Windows

There's also a manual method of copying songs from your iPod to a Mac or PC. The procedure is a bit involved and won't recover playlists but if you're interested it's available at this link: Two-way Street: Moving Music Off the iPod

You don't need to do anything to the iPod other than enable it for disk use to be able to use either one of the utilities or the manual method. If you still have the PC you can do this in advance. Once your iPod is formatted for Mac it won't run natively on a PC because Windows operating systems don't recognize Mac OS-formatted disks (HFS or HFS Plus formats). Mac formatted iPods can only be used on a PC that has a third party helper program such as XPlay or MacDrive installed.

If you no longer have the PC connect your iPod to your Mac. If it is set to update automatically you'll get a message that it is linked to a different library and asking if you want to link to this one and replace all your songs etc, press "Cancel". Pressing "Erase and Sync" will irretrievably remove all the songs from your iPod. Your iPod should appear in the iTunes source list from where you can change the update setting to manual and use your iPod without the risk of accidentally erasing it. Changing to manual update will also enable the iPod for disk use by default: Managing content manually on iPod

Keep your iPod in manual mode until you have reloaded your iTunes and you are happy with your playlists etc then it will be safe to return it auto-sync. I would also advise that you get yourself an external hard drive and back your stuff up, relying on an iPod as your sole backup is not a good idea and external drives are comparatively inexpensive these days, you can get loads of storage for a reasonable outlay.

You're welcome, I'm glad the information was of help. Take care.