External Hard drive dilemma

Hi guys, im in the process of buying a new external hard drive and I'm in a pickle...
I dont want to spent apple money on Time machines so im looking for a cheaper alternative.
ive found Western Digital My Book Live 3Tb, and i like the look of it because of the Wifi features but i don't think there is a usb port on the back so... if i decide to take the unit round a friends house does this mean i can connect the hard drive directly to the mac/pc with an ethernet cable and what are the speed differences between ethernet and USB 2.0?

You plug this device into your router, not your Mac. You won't be able to do direct connect to either Mac or PC. File transfer is via WiFi.

i know you plug it into your router, i thought maybe there would be a way to configure a wired network with it. still 100mps sounds fast enough. thanx for your help

If I am understanding you correctly you are trying to achieve a wired connection between the drive and computer correct? If that is the case the closest you will come to that is to have both the drive and computer connected to the router via ethernet cable. Anything else will involve wireless speeds for part of the transfer.