You want any decent Pentium M (Centrino) notebook for 3.5-4 hours at least using wi-fi 100% of the time and up to 5 hours with wi-fi turned off. All you can expect with a Pentium 4M cpu is much more heat, battery life likely 2.5 hours and under (depending on LCD size) and also more weight and notebook thickness.

Specify the LCD size you want. If you want a 15.4" widescreen at 6.5 pounds like I have check out the HPZT3000 and/or Compaq X1000 series at X1000forums.com and hpshopping.com

If you can do without dedicated video memory that the above has (necessary for any robust games and higher end video programs) consider the HPDV1000 which is a 14" widescreen at 5.3 pounds. It runs DVD's and CD's with the notebook turned off and has a remote control built into the PCMCIA slot (pops out).

Both of these use the Pentium M (Centrino) processors. Get at least the Dothan 1.6 Pentium M 725 or higher for the 2mb L2 system cache (lower models only have 1mb)