initdb problem

Hello people,

Having installed the universal binary for pg 8.2.4 on my mac
running 10.3.9, I'm now trying to use the initdb command,
but keep running into problems. I can't seem to get the
right syntax. Can anyone suggest where I'm going wrong?
Here's what terminal shows:

Acorn acorn 1 acorn$ login root
Password:
Last login: Thu Jun 14 13:43:54 on ttyp1
Welcome to Darwin!
Acorn:~ root# su postgres
shell-init: could not get current directory: getcwd: cannot
access parent directories: Permission denied
su: /dev/null/.bashrc: Not a directory
Acorn:/var/root postgres$ initdb -D
/Library/PostgreSQL8/data
su: initdb: command not found
Acorn:/var/root postgres$ cd
chdir: could not get current directory: getcwd: cannot
access parent directories: Permission denied
su: cd: /dev/null: Not a directory
Acorn:/var/root postgres$ cwd
su: cwd: command not found
Acorn:/var/root postgres$ /Library/PostgreSQL8/initdb -D
/Library/PostgreSQL8/data
su: /Library/PostgreSQL8/initdb: No such file or directory
Acorn:/var/root postgres$ /Library/PostgreSQL8/bin/initdb -D
/Library/PostgreSQL8/data
could not identify current directory: Permission denied
could not identify current directory: Permission denied
could not identify current directory: Permission denied
The program "postgres" is needed by initdb but was not found
in the
same directory as "initdb".
Check your installation.
Acorn:/var/root postgres$

TIA,

Joe