Instructions
Look at the back of the PS3 console and find the model number. The model number will begin with the letters "CECH."
Access the link in the "Resources" section of this article and find your PS3's model number in the chart. For the most part, if you have anything other than a 20GB, 60GB or 80GB system, you will have limited or no backwards compatibility.
Look at the front of your PS3 console and see how many USB ports it has. If you are using PS2 "Rock Band" controllers you may need to purchase a PS2 to USB converter depending on the model of the controller. Some PS3 models only have two USB ports, which means that if you want to use all four instruments, you may need to purchase a USB hub with at least two ports. Converters and USB hubs are relatively inexpensive and can be found at any video game or electronics store.
Check that your PS3 has the latest software and firmware by going to "Settings" > "System Update" in the console's menu. Your PS3 will have to be connected to the internet when you do this.
Run the "Rock Band" game by putting the game disc into the drive in the PS3.