It's interesting that the wired ones appear to work.
I vaguely remember reading somewhere that Micro$oft had built some sort of encryption into the 360 controllers to try and prevent third party manufacturers from making their own clone controllers for the 360 (yet more anti-competitive BS from Micro$oft
).I assumed this would also prevent the controllers from being used on a PC.
MS' plan from the very get go was to have the 360 wired controller available also for PC. It is part of their XNA thing.
For those that want a wireless controller for PC, I highly recommend the Logitech Cordless Precision controller for Xbox. It modifies real easy for PC (Just replace the Xbox plug with a standard USB one), and it is an excellent controller.
[EDIT]
MS didn't do anything to prevent 3rd parties from making controllers for Xbox.
They just made it so they couldn't make them without paying the licensing. MS are selling the 360 WELL below cost, and they need to actually make money on the thing somehow.