Have you gone to File > Transfer purchases from iPod... ?
I've also tried this with the iTunes Wifi store by buying an iTunes Plus song. I was slightly concerned when I had to authorise my PC iTunes in order to transfer the purchase. I thought you didn't need to do such things with DRM-free music. How can I test if my song is DRM-free? Does playing it in anything other than iTunes mean it is DRM-free?
I've also tried this with the iTunes Wifi store by buying an iTunes Plus song. I was slightly concerned when I had to authorise my PC iTunes in order to transfer the purchase. I thought you didn't need to do such things with DRM-free music. How can I test if my song is DRM-free? Does playing it in anything other than iTunes mean it is DRM-free?