Except for two Broadcom chipsets, you have to install something to make a Broadcom wireless chipset work in Fedora 12. And the thing that you have to install can be different from one Broadcom chipset to another. So it matters what Broadcom chipset you are using. Find out...
lspci -nn | grep Broadcom
When you've identified that, then the answer will come, I'm sure. It's usually easy stuff once you know what to do. Broadcom chipsets are my favorite and my choice.