Onkyo's NetTune allows you to play internet radio stations and mp3 from your home network. The downside is that the internet radio stations are only the ones accessible to Onkyo's own server - you cannot tune any old station you like and the selection is very limited.
To play mp3 requires that you install their software on your computer. It is pretty primitive. You can download the NetTune software to get an idea of what it can do.
I thought it would be a good idea but the implementation is just not good. I think its better to use another device, like an AudioTron or Squeezebox, connected to your network and then connect that to your receiver the same way you would connect any other source device. It may get better over time, but I opted to go with the 702 and forget the NetTune capability.