One thing I'm not sure about though is this: All my Thinkpads (third one now) have had Celeron processors. I noticed the other day that someone was advising people to avoid pentium 4's because they didn't run PD well. I have no experience with that but perhaps something to keep in mind.
The P4s have for instance the denormalising effect which causes some problems with audioapplications. But its not a good idea to have one in a notebook anyway because these are desktop cpus and draws lot energy. Better to go with Centrino chip(sets) so you can use your laptop on the run too.
Cheers,
Malte