Here is a quick way to install Linksys WUSB54G v1 (only tried on v1, but it should work the same way on other versions as well).
Step 1: Get the Windows driver for your adapter. You can get it here.
Unpack the file and get the needed driver, in this case it's WUSB54G.inf
Step 2: Download necessary packages. ndiswrapper-utils and ndiswrapper-common using Synaptic Package Manager or using the apt-get command in terminal.
Step 3: The easiest way to install the driver file is to first copy into your home folder (/home/username/). Now open the Terminal and type in ndiswrapper -i WUSB54G.inf. If you decide not to move the driver into Home, just do ndiswrapper -i .inf
(Modify as needed if the version is different). Next do ndiswrapper -l to make sure that the hardware is working and connected. Now run ndiswrapper -m, ndiswrapper -mi and ndiswrapper -ma.
The wireless should now be working, check Ubuntu's default Network Manager to see if it found any networks.