Here Is How I Fixed It
Leopard 10.5, Windows XP SP2, Bluetooth Keyboard (the mini one w/o the keypad)
After installing bootcamp, load the "Bluetooth Devices." It should be in the bottom right corner of the screen, or go to Start-Control Panel-Bluetooth Devices.
First, select the tab "Options" and check the box that says "Turn Discovery On."
Second, select the tab "Devices" and click the button "Add..."
Third, in the new box titled "Add Bluetooth Device Wizard" check the box that says "My device is set up and ready to be found." Click the button "Next >"
Fourth, the flashlight will search. Power on your bluetooth keyboard at this point. An icon should appear titled, "User's keyboard, New device" (Note, you will have to have your bluetooth device working in OS X.) If it does not, power on the keyboard after the search is completed and it will appear after a few seconds. Select the icon and click next.
Fifth,a box will ask "Do you need a passkey to add your device?" You can use one if you want, but I selected the button "Don't use a passkey". Click "Next >"
Sixth, Windows will attempt to connect to your keyboard. This all happens within 2-3 seconds but its crucial so bear with me. Assuming you did not select a passkey, two lines of text will appear:
Connecting...
Installing Bluetooth Device...
If both of these go smoothly and a box will pop up saying "Completing the Add Bluetooth Device Wizard." Click "Finish."
(If it does not, however, a box will appear saying that it was unable to connect. This is because your keyboard was not powered on. If this happens, start over and make sure your keyboard is powered on.)
Finally, under the tab "Devices" select the icon that says "User's keyboard No passkey Connected" and click "Properties." Under the tab "Services," a flashlight will search and a button will appear that says "Drivers for keyboard, mice, etc (HID)". Check this button and click "OK."
After a few seconds, your keyboard should work. Hope this helps!