This site describes how to find your wiimote's bluetooth (MAC) address using the Microsoft Windows XP's default bluetooth stack.

 

Go to the Control Panel
Go to the Control panel.

 

Double-click Bluetooth Devices
Double-click Bluetooth Devices.

 

Click Add
Click Add.

 

Click 'My device is set up and ready to be found' and then Next
Click "My device is set up and ready to be found" and then Next. Put your wiimote into discovery mode.

 

Click Next when the wiimote is found
The wiimote should be found. Click Next to continue.

 

Select 'Don't use a passkey' and then Next
Select "Don't use a passkey" and then click Next. If the lights on the wiimote stopped flashing, put it into discovery mode again.

 

Click Finish
Click Finish.

 

Select the wiimote and click Properties
Select the "RVL-CNT-01" device and click Properties.

 

Address is visible
The wiimote's MAC address is visible as Address.

 

Remove wiimote afterwards.
Don't forget to remove the wiimote at the end so the computer won't interfere.