For some reason there are no 64bit drivers for the Linksys Wireless-G USB Network adapter. Well, there is a work around.
Download the following driver:
WUSB54g 64-bit Driver [Zip]
Ralink Official Link [exe]
In the Device Manager, Right-click on the Wireless USB Network Adatapter and select "Update Driver Software". Follow the instructions below:
Select to Browse my computer for driver
Select to pick from a list of device drivers. From the list, select "Network Adapters".
Select the downloaded driver from disk
Select Ralink Technology Corp. & RT2500 USB Wireless LAN Driver
Click Next, and Finish. The driver should now be installed on your system.
Or you can just install Ubuntu Linux... :-D