Yeah, no joy.
Tried all sorts of permutations, but it looks like USB RT2500 devices are just out of luck on SL 64 bit.
Hmm, that's sad. But if you get this adapter ( http://www.amazon.co...r/dp/B00292BUT2 ), you can just download the USB(RT2870 /RT2770 /RT307X /RT2070 /RT3572) driver, and everything works 32/64 bit. It is the adapter I am using right now.