The Linksys WUSB54G is a USB 2.0 device, so I think your chipset or USB drivers might need updating (the former would possibly explain video card issues). Many chipsets (especially VIA and SiS) have wierd USB issues without the proper drivers installed, often resulting in some devices functioning but not others.
For working USB 2.0 support you will need the latest Windows service pack installed to begin. Download the latest chipset or USB drivers to suit the chipset in your system. For Intel chipsets visit
Support & Downloads, for VIA try
http://www.viaarena.com/default.aspx?PageID=2&Type=1, nForce go to
Driver Page, SiS
Download Center
I could also be completely on the wrong track here, so also see if you can get the device working on another computer with the same driver to see what happens.