According to the official website, NYC2012 propaganda "is privately funded by contributions from corporations, unions, individuals and foundations. No tax money is being used."
Yet there is plenty of controversy because hosting the Olympics will inevitably cost taxpayers. As usual, one must follow the money back to the "corporations, unions, individuals and foundations" that would like public subsidy of their projects.
Please let us know if this doesn't help you or if you have further questions.
Official Site and FAQs:
http://www.nyc2012.com/en/faqs.html
A good post with lots of information:
http://www.nolandgrab.org/archives/nyc2012_olympic_bid/
NYC Indymedia coverage and links:
http://nyc.indymedia.org/feature/display/151763
-tiantian