Thank you for the correction. I had heard that but hadn't verified it. The quote often stated is that the US funds the most of any other country and that happens to be 22% of the total budget, which is substantial.
Here's some interesting reading on the subject of withholding funding in exchange for a more ethical U.N.:
http://www.house.gov/apps/list/press/az06_flake/040505un.html
If the UN didn't exist, we'd probably want to invent it for that purpose alone.
None of what I just said justifies the other 99%.