I've been reading through the Wii specs and I noticed that the Wiimote communicates with the console via Bluetooth.
My guess is that Nintendo probably kept their hardware compatible with the official Bluetooth specification for simplicity's sake. This would mean that getting the Wiimote to work as a PC game controller shouldn't be too difficult. It would be a simple matter of creating a device driver.
I know that the aiming function would be a little more difficult to implement due to the sensor bar's proprietary connection, but there is another possibility: Nyko's wireless sensor bar, which I've read uses Bluetooth.
If my assumptions about the Wiimote and Nyko's Sensor Bar are correct, I should be able to hack together a Windows driver in a fairly short amount of time.
Let me know if you're interested in dedicating some time and energy to this project!