Another member found trouble with bluetooth in Windows XP. Mind you that we hope this is a real XP and not one of those cracked versions. But do read what they found at:
Windows XP PRO SP3 operating under Bootcamp on an IMAC pairs well with Apple's BT Mouse until quitting Windows. Upon restarting, Windows does not recognize the Mouse even though it is listed as a connected Bluetooth device. In each Windows session, the device must be removed and re-paired to have it work correctly.
What can be done to make Windows remember the mouse?
System:IMAC8,1, Snow Leopard, Bootcamp, Windows XP Pro SP3, Apple BT Magic Mouse