If you have access to a wireless computer that is already connected to and operating on your network, then you should go here and download this utility http://h10025.www1.hp.com/ewfrf/wc/softwareDownloadIndex?softwareitem=Im-88880-1&cc=us&lc=en&dlc=en
and then run it. Once it fully scans, click on Show Advanced Tools in the bottom left of the window and select Retrieve WPA/WEP Key, it will be on the right side.
If you do NOT have a wireless computer available, then you need to loginto your router (sorry, but I do not know which router you have) and go to the wireless page. If you have WEP, just copy down the WEP key that has the radial button selected (green dot) and that is your key. If you have WPA, copy the Preshared key.
If you do not know how to get to your router setup, go to a computer that is conencted to your router by a LAN cord. Go to Start > Run and in the Run window type CMD. If you have Vista or Win 7, go to the Start Orb and just type CMD into the serch bar. In the command prompt window type IPCONFIG /ALL now look for Default Gateway (that's your router) and copy down the IP Address.
Now open a web browser utility and type that IP Address into the address bar.