Keep getting authentication failure when trying to restore database

I have made a pg_dump of my database, and now I want to restore it on
another database. So I follow the instructions on
"http://www2.dk.postgresql.org/users-lounge/docs/7.1/admin/backup.html"
(both databases are 7.1 on Debian), but I keep getting "psql: Password
authentication failed for user 'postgres'" all the time.

I have looked in my dump file, and seen that it tries to connect first as
postgres, and thereafter as my other user that owns the tables. How do I
allow it to connect as these users? Can I somehow disable the passwords, and
how is this done?

Med venlig hilsen/Best regards
Søren Neigaard
System Architect
................................
Mobilethink A/S
Arosgaarden
Åboulevarden 23, 5.sal
DK - 8000 Århus C
Telefon: +45 86207800
Direct: +45 86207810
Fax: +45 86207801
Email: s(dot)neigaard(at)mobilethink(dot)dk
Web: www.mobilethink.dk
................................