Within "System Settings" > "Database Repository" section.
The paths on different systems are very likely to be different, following are some examples:
Backup program path: C:\Program Files\PostgreSQL\8.2\bin\pg_dump.exe
Repository for backup files: C:\Kwok\Server\FileRepo\backup
Backup program path: /usr/lib/postgresql/8.2/bin/pg_dump
Repository for backup files: /usr/kwok/filerepo/backup