If you are going to leave the notebook confined to a desk or at least a stable location consider a Pentium 4M but otherwise you should be getting a Pentium M (Centrino) notebook for maximum battery life, much thinner notebook width, much lighter weight and performance very comparable to the hotter Pentium 4M cpu.
You don't get hyperthreading but you won't get true multitasking until the 64bit 2 cpu chips come out in the future. The Athlon 64 chip notebooks are a good choice but they are still 1 cpu only and still heavier and use more batteries then the Pentium M Centrino.
It is an absolute waste to get a Pentium 4M with shared video memory.
If you don't need dedicated video memory consider the brand new HP DV1000 series which is 5.3 pounds, 14" widescreen and DVD/CD with the computer off (and built in remote control).
Otherwise, consider a HPZT3000/Compaq X1000 15.4" widescreen notebook which has up to 64mb dedicated video memory at 6.5 pounds. You will get 3.5-4 hours using wi-fi and longer with it turned off.
The DV1000 will get better CD/DVD life with its computer off feature and also the smaller LCD will allow longer all around computer battery life as well.
See X1000forums.com for all the discounts available on the ZT3000/X1000 in general as well as any HP model.
There is also a thread there that divulges the dedicated new forum for the DV1000 (a new model just last month).
Also, if you really want a desktop replacement Pentium 4M consider the hpzd7000 which is a 17" LCD model and has its own dedicated forum at zd7000forums.com