Welcome to bleepingcomputer!
You'll need the appropriate driver to make the wireless adapter work properly. It may be easier to install the drivers off the disc that came with the adapter. If you do not have the disc, then you'll have to download them off the internet.
Is the driver you found through this webpage? http://www.linksysbycisco.com/US/en/support/WMP54G/download
. I'm not sure witch version yours is though.
Are you able to download the file? If so, are you able to run the file? What type of file is it (does it end with .exe, .zip, .rar, etc.)
"I think there is a world market for maybe five computers." - Thomas Watson, Chairman of IBM, 1943