question on PostgreSQL\8.0\pgAdmin III

HI,
I am having a question on using your backup tool pg_dump.exe. to
automate the backup, but everytime it will prompt up with password. but
no matter how, I could not overcome.
is there any way to use this tool without having that password prompt. I
tried to put into perl. but perl does not understand with the prompt up.
Is there any way to do it?

C:\Program Files\PostgreSQL\8.0\pgAdmin III>pg_dump.exe -i -h localhost
-p 5432 -U postgres -F c -b -v -f
"C:\\Build\\backup\\thstadtool01-DB-$out.backup" regression -W
Password:

thanks
Steve