Adding unit gtkproc I can set fullscreen and going back (in ubuntu, not tried in maemo):

SetWindowFullScreen(Form1,true); //fullscreen

SetWindowFullScreen(Form1,false); //un-fullscreen

Now I'm playing with gtk2 unit... in "Hildon_2_2_Widget_UI_Specification_v1_0_en.pdf" I read that to show Hildon Touch View Menu I need to call:

gtk_widget_show (menu)

but I don't know how to create the menu itself...

Edit: I tried in the Nokia N900 and fullscreen works ok in Lazarus/FPC! Sometime there is a problem onClose app, no more icons in desktops if (after going back from FS) I close app with X, but if I close from windows manager (ctrl+backspace) no problem... I think I'll simply need to tweak something