I'll just pass along a few excerpts from the Congressional budget documents linked at NASA Watch. First:
Funds for announced prizes otherwise authorized shall remain available, without fiscal year limitation, until the prize is claimed or the offer is withdrawn. Funding shall not be made available for Centennial Challenges unless authorized.
The amended bill does not provide any new funding in fiscal year 2008 for the Centennial Challenges program. The funding proposed in previous fiscal years for this program is sufficient for NASA to run this prize-based competition. Providing additional funds to a program based on prizes only creates a sizeable amount of unused funds while other aspects of NASA’s mission are being cut or delayed due to a lack of funds.
This is immediately followed by 7 solid pages of "congressional directives", mostly in the several hundred thousand to low millions of dollars. I counted about 80 such juicy directives, most of which could kick off a very nice Centennial Challenge.