My god man. Broadcom and Ubuntu is not a very good combination. What Satan is said is true, but it won't work as simply as that with Broadcom.
Lucid is having the same problem I did, and I tried lots and lots of solutions, read a lot and tried those opensource broadcom linux drivers:
http://linuxwireless.org/en/users/Drivers/b43Official broadcom drivers for linux was useless too.
Shit just refused to work every time.
I eventually solved it, and it was very simple - I found the solution somewhere on 50th google page or something
Here's how I did it:
Seems that Ubuntu 10.04 does not support Broadcom fully or something, so it won't initiate the wireless device (ethernet was working fine), event tho lspci detects it. So I booted up my main Ubuntu installation as normal (10.04) and popped in the Ubuntu 10.10 CD, which I had since it came out.
When the CD gets mounted (guess it would work when you mount the image as well), Select (in Gnome menu) System -> Administration -> Hardware drivers.
It will search for drivers and give you to select which to install (for me it only one - broadcom). Then you just press on the red circle, select to use it (can't remember the exact procedure) and it should install all those drivers.
You will have to reboot after this.
Also a side note: I noticed that "Wicd network manager" works better than that default Ubuntu network manager.
Tell me how it will work for you
EDIT: Shizzle, I remembered you wanted to fix for a LiveUSB.
Sorry bro, this is when you install it to the drive.