I've not tested this, but it might work...
Set an event for "Resize" on the Form, and in that event, check the value of the form's "state" property to see if the form is minimised. If it is, set it's ShowInTaskBar property to false.
Why do you want to hide the form? If it's just because you don't want to entertain minimising and wish the button to act as a close, just set "MaxButton" and "MinButton" to false - leaving only the close button in situe... There's a property for whether or not you wish to display the window control menu in the left hand side of the titlebar as well... I mention it because Maximise etc can be called from there as well...
Hope that helps...
Martin