How to get/install/activate a Broadcom 4312 wl driver in Ubuntu 12.10

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http://askubuntu.com – i have installed Ubuntu 12.10 on my Lenovo G550 laptop. It has a Broadcom 4312 wireless lan adapter which is not working. How do I fix it. How can I see what drivers are being used. I've downloaded what I think is the driver from the broadcom site but have no idea how to get it installed. I'm completely new at this Linux stuff. I think this is the relevant info: 04:00.0 Network controller [0280]: Broadcom Corporation BCM4312 802.11b/g LP-PHY [14e4:4315] (rev 01) 07:00.0 Ethernet controller [0200]: Broadcom Corporation NetLink BCM5906M Fast Ethernet PCI Express [14e4:1713] (rev 02) (HowTos)