You have to distinguish two activities with blender, rendering and modelling. When redering, a Pentium-M is not the best. For games, it’s pretty good. The Athlon XP is not the fastest in rendering, but I don’t think you’ll suffer that much when it goes a bit slower. If you do want to render fast, you should get an A64 or pentium4-M.
As for the modelling, that’s more dependent on the videochip. You need a videochip which is able to handle OpenGL very well. Nvidia comes to mind before ATi. But for games, Nvidia chips other than the new generation, 6xxx, produce low-quality texturefiltering.
The Pentium-M is much more power-friendly than any other CPU, so I’d consider buying it, because it’s quite handy to be able to use your laptop for more than 15-30 minutes. As for Binias or Dothan, if I remember correctly, the powerusage of Binias 2.0GHz is 25 watts, and Dothan 21. It’s not that dramatic. Performance is a little bit better on Dothan, but also, not that much.