I was playing around with Ubuntu/Kubuntu 8 on my laptop. It, too, has a Broadcom-based wireless NIC that Ubuntu didn’t have a driver for. I found something (don’t remember what) that would “extract” code from the Windows driver to make it work in Ubuntu, but the bugs hadn’t been worked out of the extracting process, so I dumped Ubuntu. Everything else worked nicely, but it was pointless without a working WLAN connection.
Check out NDISwrapper. It’s a kludge, but it does work. Or get a different wireless card.