Administrative Password

I'm in need of some help figuring out what my administrative password for
Vista is!!! I work for a small company and the girl that set everything up
is no longer here and therefore we cannot access the admin accout and as I'm
sure you are all aware you can't do anything without accessing that account.
I have looked everywhere and it seems very confusing. I can get by on a
computer but I'm not professional. Does anyone know what I can do about
this...I've been at it for 2 days and would like to either just get the
password and be done with it.

Thank you in advance...