According to The Inquirer their sources, Mark LaPedus and Nathan Brookwood, Intel his Prescott has 64bit capabilities built-in but they are not compatible with AMD's x86-64 instructions.
He claims the Prescott's 64-bit extensions are different, and Intel won't implement it in this chip, but rather wait until the Tejas *T recension, which is supposed to arrive next year.
Current roadmaps Intel is showing its partners demonstrate that Prescotts will clock to 4GHz by the end of the year, with the firm talking vaguely about a "next generation" chip. Intel's problem is that it find itself in the horns of a dilemma. If it does pre-announce a 64-bit extension desktop processor, it may have a difficult job explaining just how such a chip fits in with its current Itanium 64-bit processor.
But Intel has had difficulty explaining things before when it changes its mind – with the Rambus affair being the biggest volte face in recent times.