First, a couple of specific comments.
The T42's lack of FireWire is not a serious drawback. T42 accepts 2 Type II PC Cards. Just plug in a slim FireWire card (one that doesn't stick out), and you won't notice a difference (my daughter has been using such a card in an older notebook for years without any performance or heating problems), since it won't block access to the second PC Card slot (and how needs more nowadays?).
The nc8000's SD flash reader most probably only handles cards for user authentication, etc., and not other media; I didn't have time to check, but if yes, then it's usefulness would be quite limited.
The 3-spindle design of nc8000 may still be useful for some people, but the industry has moved to 2-spindle designs.
Thinkpad's keyboards are top notch (but of course owners of other notebooks may be perfectly happy with their keyboards as well).
The magnesium cover material of T42 is an obvious advantage, as well as its smaller size and weight.
Of course, T42's 7200rpm drive is much better. If you wanted to swap the nc8000's HDD, together with the extra price and software installation hassles, you should also check how HP handles non-HP drives in warranties and repairs.
The only questionable point is whether T42's screen suffers from ghosting in the applications of interest to you. According to what I saw on the Thinkpad forums, it shouldn't be a problem to you, since you are not a fast gamer. Unfortunately you won't learn much by comparing the HP and IBM specs, since they only impose upper limits on admissible response times.
As is clear from the tone of my comments, I am biased towards the T42 here. Generally, Thinkpads are considered to be better but too costly, and this is not the case here.
Taking everything into account, I would choose the T42. Most probably, you will be happy with its screen; if not, you may return it.
On another note, you should be aware that your case is not typical for this forum, where business class notebooks are regarded as being too expensive. You should try to filter out advices given by users whose knowledge boils down to spec comparisons on cheap websites; some of them hunt for their first notebook, others have used notebooks for several months only, etc., etc. For instance, track sticks (aka point sticks, eraserheads) have been around at least since 1995, may be tapped, configured for scrolling, etc.