Implementing help on touchscreen interface

Question

Hi,

I am currently working on a Human Machine Interface, which is just a touchscreen UI which controls a machine.
Now I want to implement help on the several buttons on this UI. What I want to do is tte following:
- the user clicks on the help button (which is a normal .Net button with a help icon)
- the form will be set in some kind of Help mode
- the user clicks another button (which is also a normal .Net button)
- a small window with some help about this button will be shown

My question is the following: how do I prevent that the normal button click event is fired when the form is in this Help mode?

Thx for your answers,
Dennieku