Buying a laptop now, I would expect to have Vista on it with full 64-bit support and programs in two years and on. That makes the 64 more attractive to me for a longer useful life.
Between the two processors, the Turion will have much better battery life then the Pentium 4. The P4 will crunch numbers fast, but will act as a space heater while doing so.
I did my research this summer, and went with a Turion. I wanted portability and enjoy having five and a half hours on a charge. I can watch 2 DVDs, so long as they are not Harry Potter.
Wetzel