Joachim
I can only suggest that you try to set up the site again from scratch. This may prove an easier solution. With windows systems it is always best to set up everything manually rather than using any installers. I suggest a manual configuration of PHP version 4.3.11 with MySQL 5.0.19 and Moodle 1.53 stable. If it would be of any assistance, the following may help in this regard:
http://s7.quicksharing.com/v/4329398/cms.zip.html
This is a training package for full manual install under IIS or Apache. I recommend Apache version 2.0.55 win 32 no ssl
Steve Henderson