If it has Lion or Mountain Lion, do a command-r boot to Recovery and in the Utilities menu you will see a password reset utility. If it is an older OS, you can find the same utility by booting to the install DVD.
It is X10.6.8, I think "Snow Leopadr", the seller say: "There is no password, just leave the space blank". I'll try your recomendation. I'm trying to load "Boot Camp" so I can load some of the software I have that I used on XP. "Boot Camp" is asking for a password.