Thanks to the fabulous nerd power of Mefi users, I have an answer.
MC Miker G and DJ Sven's "Holiday Rap" is the jam in question.
If you already weren't sold on the track alone, check out Miker and Sven's totally hype promo glossy:
Fan fucking tastic. Now watch the video. Tell me the beatboxing sequence isn't the best thing you've seen all week. These guys are easily the greatest and best dressed rappers of all time.