It's a Linksys product. Even if Microsoft comes out and says "it should work", it is Linksys' choice whether or not they choose to support it.
Official Product Page:
http://homesupport.cisco.com/en-us/wireless/lbc/USB300M
You might *try* the instructions for connecting it to Vista - but it just may be time to spend the $25-$75 and get something that doesn't mention USB 1.0/1.1 or Windows 98SE/ME/2000 like they should still be supported (or that you need at least a 200Mhz processor.) ;-)