In laptop situations, usually battery life and weight are very important. If you already know what weight your laptop is going to be, and are having trouble choosing between the Celeron or Duron, you need to take into account 2 factors:
1. Battery life.
2. Types of apps being run.
If you get the Mobile Duron (Morgan core, PowerNow technology) your battery life will be inferior to that of the Mobile Celerons (Tualatin core, SpeedStep technology). Even though AMD's PowerNow technology is superior to Intel's SpeedStep technology, mobile Celerons in general have significantly better battery life than the Mobile Durons due to the silicon process that is implemented (the Celeron has a small .13 micron process compared to the Duron's larger and hotter running .18 micron process).
If you get the Mobile Celeron your performance will be inferior to that of the Mobile Duron. For example, in most types of video games and most scientific and integer related apps, the Mobile Duron will perform better. This is mainly due to the differences in architecture between the Duron and the Celeron.
So, if battery life is the most important thing for you, go with the Mobile Celeron. If performance is most important for you, go with the Mobile Duron.
IMO, I'd go with IBM or Dell for your laptop. They don't sell any mobile Durons or Athlons, but they have a great selection of Pentium III and Celeron powered laptops. For good, solid laptops using Mobile Durons or Athlons, go with Compaq. HP is also very good as well.