Out of curiosity, I booted off my Leopard DVD that came with the Air (10.5.6), and it also saw the disk attached to the Airport Express for Time Machine restore. So from what I can tell, it's worked pre Snow Leopard without config changes, but may not be fully supported by Apple. Confusing to say the least. Some reports say it started working at 7.3.1.

I don't have Bonjour installed in Windows 7, and see the disk fine in Explorer just like any other share on the network.