Reports are that since Bootcamp version 3 or so you can now read and write to the macintosh partition from your windows environment. This is less than ideal in a shared computer lab.

Renaming the file:
c:\windows\system32\drivers\applemnt.sys
and then restarting should disable the mount of the macintosh partition in windows …

For more discussion and details see:
https://discussions.apple.com/message/11226479?messageID=11226479#11226479?messageID=11226479