some problems about qvfb

hi, i just intall the QtopiaCore-4.2.0-tp1 under ubuntu 7.04, the
path is:
:/usr/local/Trolltech/QtopiaCore-4.2.0-tp1/

any one can tell me how to set the enviroment varible?

and there some problem about qvfb, when i enter this:
qvfb

../mainwindow -qws

the output in the framebuffer is not correct, the screen always flash
when i move mouse on it.

.