Hi, I know this is an old topic but it's nice to see my old DirectX rewrite of The Grodan and Kvack Kvack demo get a mention on a thread with Tanis!
Link to implementation details:http://www.lynn3686.com/techtech_inf.html
The tune is in the zip file, it is called ronken.mod
I know that it might not run on some new graphics cards, which leads me to the point that if I convert more demos to the PC I should make them able to run "in a window" in a hardware independent way.
Still got, still working: Atari 4Mb STe, 520STFM, 2.5Mb STF.
Hardware: Cumana CSA 354, Ultimate Ripper, Blitz Turbo, Synchro Express II (US and UK Versions).