Speed of my application

Hi,
I have an application with 6 form classes.
I set the following:

FormX->showFullScreen();
FormX->setVisible(false);
(x := 1 .. 6 )

The user can change the visibility of forms with the GUI (using icons). During the changing a green background appears. This takes for 6 second. How can I remove it?
Are “6 forms” a good solution? These forms are inherited from Qwidget.
My program is a bit slowly. IS there any kind of trick to speed up?
For example:
Starting networking, web server takes 4-6 seconds. (When I switch on the mini2440)
Using the tabs of tabwidgets takes 2 seconds.
I use many threads. Can be any kind of effect on each other?
Thanks, David