low power consumption means the atom cpu right now. ive heard they are considered to be similar to an old P4 2ghz in terms of horsepower. as long as your mom is not ripping dvds for a living they will work ok. these are best for computers that remain on 24/7 where the saving will add up.
http://www.newegg.com/Product/Produc...e=Intel%20Atom
the thing that throws the above off is that newer mobos and any intel wolfdale cored cpus idle at stupid low watts. i just went this "caged lion" route myself for a 24/7 'puter.
http://www.xbitlabs.com/articles/cpu...lfdale_11.html
its a cool time for computer these days. 300 bucks can make something great for the average user. gaming still costs a arm and a leg though lol