Well, you indeed do not need any password for your wireless printer to connect to your laptop pc. If its a first time configuration, then you need to configure it with the USB cable and hence it would let you connect wirelessly.
Take help from e-how: http://www.ehow.com/how_2192712_setup-wireless-printer.html
Lusinevahe, you can get the WiFi password for your network from the router's configuration utility on-screen.
Look in the wireless section >> security and the WiFi key should be shown there.