help pls, UIbuilder preview window is all black
 

Note: english isn't my firts lang so excuse my spelling errors.

I'm noob in making ui, trying to make a UI... But when i load a default UI piece the preview window in uibuilder is black.... there is a way for it to show the ui piece there? help pls!!!

You need to make a full copy of Default folder in your EQ2/ui disrectory.
Then open (if I remember right) eq2ui.ini or something
this will load all pices

eq2ui.xml shows but i want to see eq2ui_mainhud_pet.xml.. what i need to do to make that piece shows in the preview?

You need to go to MainHuD tab. But from screen shot you included you just opened eq2_mainhud_pet.xml not whole eq2ui.xml as you should.

so i edit eq2ui_mainhud_pet.xml in the eq2ui.xml mainhub?

Open EQ2ui.xml

Whence opened go to the MainHUD tab and on the left expand MainHUD page, from there go to the "Pet" page and bring it ^up^. You should beable to edit/see it, as well as all the other windows.