64-bit will be 'in' in 2-3 years, by that time, there'll be much greater CPU's that will romp the AMD64's out right now. And besides, the AMD64's use about 3 times as much power as the Pentium M, and in many cases the Pentium M outperforms it in the usual Intel fields, i.e. Video/Audio Editing/Encoding. And if you ever want to watch a DVD on a Pentium M, they're optimized up the rear for that, Intel was really thinking when they released the Pentium M.
Go with the Pentium M, you won't be disappointed.