Cita: This is the first PostgreSQL release to run natively on Microsoft Windows® as a server. It can run as a Windows service. This release supports NT-based Windows releases like Windows 2000, Windows XP, and Windows 2003. Older releases like Windows 95, Windows 98, and Windows ME are not supported because these operating systems do not have the infrastructure to support PostgreSQL
Como ves el Windows 98 no es soportado por postgres (aunque puedes forzarlo haciendo un initdb manualmente, pero no es recomendable!, otra opción es usar Cygwin o cambiar de SO xD).
Saludos