Вот пример на делфи:
procedure TForm1.TrackBar1Change(Sender: TObject);
var val : integer;
begin
val := TrackBar1.Position;
SystemParametersInfo(SPI_SETMOUSESPEED,0,Pointer(val),SPIF_SENDCHANGE);
end;
константы:
SPI_SETMOUSESPEED == 113
SPIF_SENDCHANGE == 2