BUG #3930: initdb failed - "postgres" not found

The following bug has been logged online:

Bug reference:      3930
Logged by:          Markus Eisenmann
Email address:      markus.eisenmann@gmx.at
PostgreSQL version: 8.3.0
Operating system:   Windows XP SP2 - german
Description:        initdb failed - "postgres" not found
Details:

After a successful installation, I want to initialize
a new db-cluster using initdb.

I've got following message:
The program "postgres" is needed by initdb but was not found in the same
directory as "C:\Programme\PostgreSQL\8.3\bin/initdb".
Check your installation.

The file postgres.exe (3.661.824 Byte) is allready there and would be
executable ...

Grretings from Austria!