Linksys Wireless-G PCI Model WMP54G

=Broadcomm BCM43xx Driver=

Easy Way
System -> Administration -> Hardware/Additional Drivers, then activate the Broadcom BMC43xx driver.

Disable your wired connection and test the wi-fi.

Troubleshooting
Full Instructions Are Here (https://help.ubuntu.com/community/WifiDocs/Driver/bcm43xx).

Determine the Driver :
 * Open terminal and type in "lspci -v" (Lists all PCI cards in verbose).
 * Find the wireless driver listing and verify the chipset (Broadcomm BMC43xx was used in this example).
 * It will look similar to this : "03:00.0 Network controller [0280]: Broadcom Corporation BCM4322 802.11a/b/g/n Wireless LAN Controller [14e4:432b] (rev 01)"
 * If the driver is not Broadcomm BMC43xx look into the Helpful Links for additional information.

Helpful Links
List of Linux Compatible Wireless Drivers : http://linux-wless.passys.nl/query_part.php?brandname=Linksys

Another list of Linux Drivers : https://help.ubuntu.com/community/HardwareSupportComponentsWirelessNetworkCardsLinksys