Delete files from the NAS (user rights problem)

I have a big NAS at home with files on it from all family users with their own user names and passwords.
Of course some of those have been changed in the last few yeats due to loss of password etc.

Everybody has just dumped their stiff on the NAS and now that I want to clean it a bit I cannot delete the majority of the files on the NAS. No user rights.

I am logged in as an admin. I tried it with Windows Explorer, Total Commander and I even went as far as executing the cacls.exe command. I cannot delete it from a XP 32 bit, and even when I run Windows Explorer as an admin from my Vista 64 bit it refuses to delete it.

Any ideas how to clear all user rights so I can clean it up asap?

Thanks
Peter