The PS3 needs to be connected to the network rather than the PC. If you have a wireless router it should automatically find the network. If you have a wired connection the PS3 will need to connected to the wall socket via the ethernet cable i.e. If you only have one internet connection the cable which usually connects to your PC will need to be connected to the PS3.
I would suggest getting wireless if you dont already have it. Lots of Internet providers give free frouters now. I have one from Sky.