BUG #3895: Access denied

The following bug has been logged online:

Bug reference:      3895
Logged by:          Arjan Bolmer
Email address:      Arjanbolmer@hotmail.com
PostgreSQL version: 8.2.6
Operating system:   Vista
Description:        Access denied
Details:

I tried installing Postgres 8.2.6, everything went fine but then all of a
sudden i got the message "Acces Denied Cannot create user 'postgres'".

Is there any way i can solve this or has this been fixed in another
version?
I have to use postgres for school so any way or another i have to make it
work.