Adding a new HDD

Hi, two years of steam sales and school have resulted in my 1tb drive becoming full. Im in need of a new drive, ideally around a terabyte that i will use to store my steam on (approaching 500gb). Im unsure what needs to be done to achieve the physical upgrade. Is it a simple case of plug in a new one or will i need to be concerned about power requirements and such. My system is on windows 8 64 bit ( i know!) and is currently home to an i7 860 3.5ghz, gtx 670, 8gb of veangance ram and a 650 watt bronze power supply. The current drive is a wd caviar green 1tb 7900rpm 64mb cache. What will i need cable wise and what drives to you recommend for running steam of (large ssds are out of budget). Looking to spend around £100 (hopefully less). Thanks