The kernel 2.6.24-14-generic works fine. In the 16-generic kernel that 8.04 has there is no wlan0 interface. Seems this is the problem, not the with the networking per see.
lshw -C network
description: Wireless interface
product: BCM4312 802.11a/b/g
vendor: Broadcom Corporation
physical id: 0
bus info: pci@0000:10:00.0
logical name: wlan0
width: 64 bits
capabilities: pm msi pciexpress bus_master cap_list ethernet physical wireless
configuration: broadcast=yes driver=ndiswrapper+bcmwl5 driverversion=1.45+Broadcom,10/12/2006, 4.100. ip=HIDDEN latency=0 link=yes module=ndiswrapper multicast=yes wireless=IEEE 802.11g
This is an upgrade from version 7.