If I understand the way the Chocolate works, you should be able to use it. You will need to by a micro SD card and a card reader. You should be able to mount the micro SD card and drag MP3s to it. It won't play AAC files. It will play certain DRMed WMA files downloaded from the VCast Music Store. And regular WMA.
If you want a slicker way of doing it, you might try a nice piece of software called SyncTunes to sync tracks/playlists to SD cards (not for the Chocolate, though). I think it's freeware. Nice interface.
I don't believe that you can connect the Chocolate directly to your Mac, even with the 29.99 dollar Music Essentials Kit (cable, stero headset, Windows software). However, Verizon Wireless has a 15 day return policy as long as you have the packaging and the receipt so you could always try.
You won't be able to access the Verizon Wireless VCast Music store from your Mac, though, if you wanted to, you could download songs directly to your phone. Kind of expensive, though.