It appears there is a compatibility issue with installing PostgreSQL 8.3 on some Microsoft Vista machines. If you encounter the "Failed to initdb" error message you may need to install PostgreSQL 8.2.7 until the developers at PostgreSQL are able to resolve this issue. Below is a download link:
PostgreSQL 8.2.7
Download the above file. Unzip it then run the file named "postgresql-8.2.msi".
Note: Remember the password you enter for the username "postgres".
Best regards,
Derek