How to prevent task manager from minimizing or maximizing my window?

I never thought it could be solved that way.

As I see this is is the most iniversal solution :)

Thanks a lot !!

I have one problem left -- the thread I've added consumes 100% of processor time even if created with IDLE priority. What shall I do to prevent the thead from eating all processor's time:confused:

You've just ou've discovered the problem with that approach. The thread has to sleep most of the time, to avoid killing the performance of the whole system. If it wakes up too often, it will be a performance drag, if it doesn't wake up often enough, it will flicker or worse.

If you don't add any code, other than checking the window status between sleep cycles, you could try a short interval and see what the effect is (look at the performance monitor, as well as the screen).