Ralink wireless adapter for my power mac won't work

I bought a Ralink dual band wireless-n USB adapter for my Power Mac G5 so that I could connect it to my wireless LAN . It came with a mini cd with the drivers but since my Mac doesn't have a cd drive I had to download the driver from the net and load it. I went to the Ralink website and by a process of elimination downloaded what I think is the right driver and loaded it onto my mac. Now I have a Ralink folder in the application folder on the mac but when I try to launch the application I get a message saying that it isn't 'supported on the architecture '. When I plug in the adapter into the USB slot nothing happens. My Mac is running OS X 10.5.8. Any suggestions ?