I took delivery of my Linksys WUSB600N V2 today and was very excited to get my G4 Mac Mini online. The many online sources suggests all I need to do is change a few values in an Info.plist. However as it turns out, that wasn't enough. In order for me to get it working, I had to change the values, but also write the new values in hexadecimal format. This is because even though 0x0079 translates to 121, that is only true for a little endian system. Likewise, 0x1737 also only translates to 5943 under a small endian system. Since OS X running on PPC is a big endian system, unless you write out the exact byte values using hexadecimal notation it isn't going to work.
So, for the record: Linksys WUSB600N V2 runs just fine on OS X 10.5.8 running on G4. It does 5GHz and successfully authenticates with my airport express, which the Monoprice USB 2.0 Wireless N it replaced didn't.