1) Copy your entire calibre folder (library) to a usb stick
2) Find your calibre settings folder (optional) and copy that to the usb stick as well. You can find it by going to Preferences =?Miscellaneous and clicking the "Open Calibre configuration directory"
3) Install calibre on your new Pc
4) Copy the contents of your settings folder from your usb stick into the settings folder on your new installation (optional)
5) Copy the library to the desired location on your new Pc
6) Open calibre on your new Pc
7) Click Library=>SwitchLibrary and then click the Browse button to locate the library you've just copied over.