A while back we already wrote that Intel might use a 533MHz FSB for their budget Prescotts and now VR-Zone says they have some proof of this in the form of an Intel Engineering sample :
Strangely, a 533Mhz FSB Prescott processor clocked at 2.66Ghz has been spotted which is no where in the Intel roadmap previously. An earlier report at TheInquirer revealed that this processor is meant for the value segment and is packed with only 256KB of L2 cache to be available in Q2 of next year. Interestingly, Intel has decided to let 533Mhz FSB to stay on longer and it is unclear if the 533Mhz FSB Prescotts are HT ready.
Source : VR-Zone
, a photo of the back can be found here