Another precaution for an admin:

make your passwords very strong:
use 8 characters or more, upper and lower case, numbers, symbols, no words or logical things.

After you did that:
Dump the SAM file -> you now have the hashes ->
check with l0phtrack 3.x how much time it takes on a fast computer to crack them. -> Set the time that users have to replace their passwords to that time or less. -> You passwords get replaced before they could be cracked.

and of course disable not used accounts, they could be a vulnerability.