Can't get Playon to show up on WD TV Live

I just got my WD TV Live and I’m not having a easy time at it. I don’t have a separate storage device hooked up yet I’m waiting for  My Book Mirror Edition 2tb to arrive. I downloaded the Playon program but can’t seem to get it to show up on my WD TV Live. I have a network connection and can use You Tube.

I’m at a loss do I need the external drive for this to work? Also I can’t view any files from my computers hard drive, do I need the external drive to do that also. I am running Windows XP Media Center Edition.

Thanks, Andrew