Martin,
When you run minstall for Timidity, it shows 1 item to select. Hit the number '1' and the item will show <selected>, or hit the number '1' again and it will show nothing. When it shows nothing, hit enter. See if that uninstalls it (after a reboot).
I had trouble with this some time ago, and ended up manually editing MMPM2.INI to get rid of Timidity MCD.
Regards,