If you want to know where to download the latest drivers, then try here:
http://www.microsoft.com/hardware/mouseandkeyboard/Download.mspx
If you're looking for the latest updates to those drivers which some people
have been saying are out, then theoretically, those should come down via
Microsoft Update (note that Use Microsoft Update is an option under Windows
Updates -- it checks for other MS updates than just the OS stuff). I assume
you have to have some form of the drivers from the link I provided loaded
for Microsoft Update to pick them up.
