external hard drive

I'm looking for a external hard drive for my grandmom to backup her computer to preferably around 80 gigs or so and it has to have a setting in it that it backsup the computer automaticly

for that you don't need any special software or special external.
you can get a 120GB drive and put that in a USB casing.
From there u can even use windows backup utility, of if u dont fancy that you can google for a freeware backup utility