somehow they enabled the administrative option in your pc .
they must of networked it to anouther pc perhaps .
now they have you locked out from managing stuff on your pc .
(double check this by trying to install a different program)
try right clicking on network neiborhood , and check in "access control "
also i think you can unistall network neiborhood and then reinstall it . you will have to reset the protocals if you do this though or you will be open for intrusion from the internet .(unless you have a good firewall)
another thing is that they may have set your security settings up to high also .(just guessing here )
you can also edit it out from the regedit , i just dont remember exactly were it is at the moment (Darn cold has me feeling like the coyote after an anvil hit him)