I am getting my RasperryPi Rev2 soon, and I plan to use it as a media centre. I have a WesternDigital Elements 1TB USB3 2.5" USB powered external harddrive. I know that a normal USB port outputs 500mA, and the Pi recommends 700mA in. 

I was wondering if I bought a 1.2A PSU, will that be enough to power the external through the RPi's USB ports?

I was looking at this power supply.

[Micro USB power supply adapter,Euro,1.2A](http://za.rs-online.com/web/p/plug-in-power-supply/7263053/)

Thank you for your help.