If you don't own one of the earlier PS3 models you have to reinstall the system software in addition to replacing the hard drive.
Here are some instructions for you to follow: http://us.playstation.com/support/answer/index.htm?a_id=362
Just follow the instructions for: "For 40GB (model# CECHH01), 80GB (CECHK01, CECHL01), and 160GB (CECHP01) only" and you should be fine. Your system is simular to those models.
To complete the process you need to download the system software to a flash drive with a PC, the details on how to do this in also in the instructions...