The 4312 card is usually reckoned to work best with the broadcom-wl driver. Some, but not all, 4312's will work with the b43 but it's not guaranteed.
If you want to install the broadcom-wl rpm's from rpmfusion without an internet connection then you need to know which kernel you are running.
from a terminal will tell you that. My machine reports:
Go to this site if you have a new install that you have not updated:
If you have managed to update then you need to go here:
You will need a file like:
but that matches your kernel number and architecture, the parts I have highlighted red, and a file like:
note how the parts of this file name match the previous file, and finally like:
that again matches the other two. Don't worry, the architecture for this one is the basic architecture.
Transfer them all to a folder on your linux machine where there are no other rpm files..
In a terminal, acquire full root rights by issuing the command:
that's a space and a minus sign after the su.
Then use the cd command to change into the folder where you have the three rpm files.
Use the command:
to install the three files. By using a wild card they should be able to sort out their interrelated dependencies for themselves.
That should get broadcom-wl installed.
At that stage, NetworkManager in the notification area of the panel to the left of the clock "may" begin to identify wireless networks when you left click on it.
If not, then in the same terminal window as you used above run:
service NetworkManager restart
Do be sure to get the parts relating to your exact kernel. Theres an 'i586' and an 'i686-PAE' mixing the various bits can lead to unwanted complications.
The notes refer specifically to Fedora 11. They should translate fairly easily to F12 just by substituting version numbers in both the commands and the links to the rpmfusion site.
Usually, the b43 driver is well mannered enough to get out of the way of broadcom-wl, but if it doesn't then we may need to blacklist it.
Post back if you have any questions or problems.