From reading the reviews in the last several months I have the impression that Intel is right now having a clear lead over AMD and it seems that this is not going to change for the next many months. So I would suggest you to buy the fastest Intel mobile processor with the faster Front Side Bus speed and the largest cache you can afford.
Also, I heard that today's Intel Core 2 Duo processors are extremely good at overclocking. I have a friend who runs his 1.8 GHz processor at 2.7 GHz. Another runs his 2 GHz processor at 3 GHz.
So if you are into that, you might want to look around for a laptop that is overclockable. There is one I know of: Dell XPS 1730 but probably there are others.
If I were you I would not settle for less than 2 GB of RAM but 4GB would be even better if you still want to have a fast machine 1 1/2-2 years from now.
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