Amazing, that great number of replies on my questions about the Casio keyboard. Especially the efforts of everybody to make me clear what 's going with this sort of things. I realised that I knew to little about this subject before I wrote the first memo.
In the meantime, after having studied your reactions and a lot of mails and websites, I managed to record the music, played on the keyboard.
The positive result came out a configuration of:
1. a normal midicable between the keyboard and the 15-pins connector of the soundcard (=Sound Blaster); a computer with Windows XP!!
2. installation of Quartz Audiomaster software;
3. resetting / changing of the data in the Audio page of the Config.screen;
4. Following the instructions of the Casio Europe webpages about Connecting your Casio keyboard to a computer. See these pages via the link: http://music.casio.com/e/data_ex2/connect.html .
By the way: you can discover that I did not use the before mentioned interface "MD1003 USB-MIDI". This interface should be used with a more modern computer (Vista or Windows7).
Thanks you all for the support. Frans