thx for answeres.
i tried out the things you suggested but somehow it doesnt seem to work.
example: i work on a pc with winxp on it. i know that another pc in the lan (also winxp) has no password set for the default "Administrator" account.
with net use i try:

net use x: \\computername\c$

then i get: blablabla please enter username for COMPUTERNAME\GUEST: computername\Administrator

blablabla password: <nothing>

Username or Password not correct ....


The same happens if i use the login-username and pwd from that pc (ex: john:smith)

thx for answeres