ipod -> iTunes -> New Mac from PC

Hello everyone.

This is my first post here. I did do a couple searches but didn't find anything that would answer this question.

I just bought a mac. This is my first mac. So everything I have done with my ipod and itunes was on my PC.

I have authorized this computer (3 out of 5 computers authorized).

I have authorized a few single songs that were purchased from itunes.

I can play them on my computer but they will not move to my ipod. It gives me the error that "x" number of songs can not be moved to ipod because you are not authorized to play them.

I can not see anything else I can do. There must be a simple step I am missing here. Could this have something to do with the fact that I have not formated my ipod for the mac?

I have thousands of songs (and dollars) purchased from itunes that I can not play on my own ipod.

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Side question...
I used the "check out" feature on my PC. I can not see how to set that up in itunes on my mac. This is how my kids place music in itunes for me to check out before they buy.

Thanks for helping a mac newbie!

Rob