Update Mar. 9, 2010. Readers pointed out that I should have said that this fix is for the only Apple-approved Windows solution, BootCamp. However, I understand that a hack at Uneasy Silence will work on Windows XP installs. DM
A recent Apple Support Note says that "certain features" on the new Magic Mouse and the Apple Wireless keyboard are having trouble in Windows on Boot Camp. A fix was posted for downloading late last week.
Certain features such as up-down scrolling on the Apple Magic Mouse and brightness controls, volume controls, the Eject key, and the key combination Control-Alt-Delete on the Apple Wireless Keyboard (2009) may not work with Boot Camp.
The fix is the Bluetooth Update 1.0 for Windows and must be downloaded to your copy of Windows XP or Vista running in Boot Camp. Hey, not a word about System 7.