python + qt question

Hello,

I am new to PyQt although I have a very good knowledge of php.
I have an application built in php and I am trying to
convert it to PyQt. It uses a Mysql database to store and
retrieve information about our company's work process.

Anyway I am using it as a project, in order to learn PyQt.
Initially I have two questions.

1. I made some menus in Qt with Qtdesigner [File (new,open,etc)]
and I would like to know how can I display different screens (not new windows) each
time one of them is clicked (in html terms, change the source of the page)

2. Is there an equivelant for the html frame tag for Qt?

Any help would be appreciated.
Thanks