The screen issue is to do with your video card, backtrack's drivers for said card, and your screen's capibilitys. I cant help you much on that.
On bootup you should just be able to leave it (dont touch anything after booting), or perhaps press enter. Either way, whatever the default option is should be fine.
"i need more than one command screen." -- If you are running a KDE-like desktop, find the "terminal" application from the applications menu. Thats your command screen... you can open as many as you want.
Hope that helps, im a wee tad rusty on bt3 (it doesnt detect my ethernet card
) so i havnt used it for a while.