Severed's right. I haven't found any reliable, automatic way of pairing the Wiimote on boot of a PC.
There's several theoretical approaches floating around, but I've never gotten anything to work reliably and consistently. From what I can tell, the Wiimote +IS+ bluetooth, but not 100% kosher bluetooth. They do some things with respect to the wii console that you just don't normally do with PC bluetooth devices.