See the bugtraq archives (search for 'bugtraq' on Yahoo) for
information on what is vulnerable and what isn't. Also, if you
have a commercial OS, why not ask the vendor whether they are
vulnerable?
If you have a Linux router/firewall, you can protect machines
behind it from teardrop by setting the router to 'always
defragment' when compiling the kernel. Apart from Linux, I
think only Windows95/NT is vulnerable to teardrop, but as I
say, check the archives if you care.
-- Erik Corry erik@arbat.com