Hi, guys!
I am planning to buy a notebook HP Compaq nx7400 EY508ES and install Slackware 11. On the internet I have found some info regarding so called "bad state" problem for nx7400 series. Have anyone experienced this problem and how can it be solved? What other possible problems can emerge in Linux and in Slackware particularly on this notebook?

This is a general answer, but if you have physical access to the notebook you could try booting it with a live cd or dvd distribution such as knoppix or slax. If it boots with the live dvd then it can run linux - or maybe that should be: linux can run it At least that's been my experience.

Also, in case you haven't checked it http://forum.notebookreview.com/ has (or at least has had) a fairly knowledgeable bunch of regulars - a good few of whom use linux on a wide range of old to current laptops. Anyway they might have already discussed your very question. In fact they might even inspire you to look into buying a non-branded laptop (as the linux-on-laptops book suggests too).

Good luck in your search.