This is a really easy fix and you do not need ethernet to download the drivers or firmware. They're on the live CD/DVD. Since you have no ethernet it'll be easier to go into a live session, get the wireless going, then immediately install the OS while the wireless is working.

Open a terminal after you boot from the LIVECD and go to additional drivers. Select the STA driver. Once it activates, which it will right from the CD, it will prompt you to restart. DO NOT RESTART! Simply open a terminal and
sudo modprobe wl
Wait a few moments and then try to connect.

Once you connect, install the OS during that live session. Once it finishes you will have a live working wireless connection on your first boot into the newly installed OS.