You can search Amazon or Bestbuy or whatever your favorite site is for "Wireless Access Point" -
Here is one for an example. There are cheaper ones (wireless G) but wireless N is the newer/faster/better type. It will come with a setup CD, you'll probably just have to plug it into your cable modem/router via an included ethernet cable- then follow the setup CD and it will walk you through setting up the access point and securing it with a WPA passcode. Then on PS3 you setup wireless network settings, put in the network name and passcode, and you should be connected.