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.
pd used to have problems with denormals until version 0.36 ... since 0.37, denormal handling have been implemented ... the devel_0_37 branch is using assembler coded simd instruction that are not that critical concerning denormal numbers ...
on some p4 cpus it's even possible to switch on DAZ which causes the cpu to handle denormals as zeros in simd instructions ... i'm not sure how different operating systems handle this, but i _suppose_ this explains problems i had when switching from suse to gentoo and got stuck in denormal crashes ...
anyway, a machine that is not affected by the denormal problem is not as important as it was about one year ago if you are on pd ...
cheers ... tim