I'm not sure what wireless CD you are referring to. If you mean the Ubuntu live CD, then your wireless won't work without the firmware on that either. I read that once you have Ubuntu installed, you can go into the System-->Administration-->Restricted Drivers Manager, and there will be an entry where you can enable the Broadcom driver (and firmware?).

How big is the hard drive in your PC (I assume it is a laptop)? Also, how much of the disk is Windows using? We can then determine if you can create a new partition for Ubuntu.

I don't understand why you cannot connect with a wired LAN connection. If you have a wireless modem at home, it should also have a few inputs for wired connections. Maybe you can connect somewhere else, like school, library or a friend's house. You only need the connection long enough to fix the wireless.