Problem editing pg_hba.conf on Vista

When installing 8.3 on Vista, we are having a problem when we change the pg_hba.conf file to allow trust authentication. This worked fine on Windows XP. However, after making the change and stopping/restarting the  service, we see an error in the Windows Event Viewer that says it no longer cannot open the pg_hba.conf file, permission denied.  Vista also seems to lock these config files in a way that prevents them from being removed even after uninstalling postgres. Has anyone encountered this problem and found a solution? Thank you.

The relevant part of the file now looks like this:

# TYPE  DATABASE    USER        CIDR-ADDRESS          METHOD

# IPv4 local connections:

#host    all         all         127.0.0.1/32          md5

host    all         all         127.0.0.1/32          trust

# IPv6 local connections:

#host    all         all         ::1/128               md5