First of all N series boxes are nothing new, they've been around for quite awhile, but were typically around for sale to resellers to would want to rebrand them.
The pricing difference is quite simple to explain on Dell machines. One of the ways OEM's(not just Dell) are able to sell thier machines so cheaply is that they load more than just windows on the machine. All that software that comes with the machine was either given to the OEM for free, because having a "lite" version of something installed on somebody's computer is a great way to generate upgrade revenue, or money was paid out to the OEM for the software to be included. This has to do with why Dell computers come with Roxio now instead of Nero or Easy CD, they got a better deal from Roxio. In addition to the OEM's getting this software for free or getting paid to put it on the computers sometimes they get a kickback whenever the customer upgrades. AOL for instance...when you sign up for AOL using the free trial included with your computer your OEM will eventually get a kickback. In the case of some of the machines, especially at christmas and other major sale times, an OEM might sell machines at cost or below in order to make money off of just extended warranties, the software kickbacks, and accessories sales.

And for those of you who have to find a way to slam microsoft and major corps in every single post remember that since both Dell and HP/Compaq both charge for software support selling a PC full of microsoft and other products that are likely to generate support calls is a great long term source of income ;-)