If I remember correctly, all I did was have my HTPC turned on and I opened up Windows Media Center. Because both the HTPC and the Xbox 360 is connected on the same router, once I turned on the 360, WMC automatically recognized the 360 as an extender device and from the 360 I was able to view all my pictures and videos that is on my HTPC. I guess this would be useful if the Xbox 360 was in another room and I was connected to the network router using a wireless device on the 360, but since it's on the same router sitting right next to my HTPC, it sort of defeats the purpose of having the 360 as an extender.
I don't know anything about the PS3, but you can probably use TVersity -