Changing Previous Owners Name

As most know,I work at a pawn shop cleaning up bought computers, or those that were lost in pawn, for resale. One of the many things that I do, since I can't reinstall but rather have to work with what comes on the machine, is eliminate all accounts but one administrators account which I typically name "owner." To keep these machines safe from mischievious children and other would-be "messer-upers" on the sales floor, I password protect the screen saver. This also provides an opportunity for the salesperson to get involved. Anyway, when the password window opens, it still has the former owners name�the registerer�in that window. Isn't there a line in the registry listing that name? Can this be edited in the registry.