In case there's any doubt, the US Embassy website says:
The Enhanced Border Security and Visa Entry Reform Act passed by the U.S. Congress in 2002 does require that all persons traveling visa free to the U.S. under the Visa Waiver Program have a biometric chip identifier in their passport by October 26, 2004. Those travelers who use passports issued after October 26, 2004, that do not contain a biometric identifier, will be required to obtain a U.S. visa. That visa will contain biometric information. Those UK travelers who use machine-readable passports lacking a biometric chip but issued before October 26, 2004 will be able to continue to use the Visa Waiver Program until that passport expires. The U.S. Government is aware of the concern among officials of Her Majesty's Government caused by this deadline. UK officials have made clear that they do not anticipate that they will be able to begin issuing passports with biometric chips by that date, raising the possibility that some UK citizens will need to obtain a tourist/business visa for travel to the U.S. We are old friends and long-time allies, and the U.S. Government remains committed to facilitating legitimate travel to the U.S. We will continue to work with Her Majesty's Government in pursuit of a solution to this problem.

So there! The bold bit is the bit I'm interested in, as I'm hoping to go to Mount Airy in June on a two year old passport.
Ray