I know that this has been gone over a million times, but i have to ask.
i am using prem pro and am trying to take a 16x9 project and slap it into a 4x3, ultimatly getting a letter box'd version of my project.
i just started using pro, i have been a 6.5er for far too long.
in 6 and 6.5 i remember that it was a simple as opening the widescreen project in a standard project and clicking maintain aspect ratio.
i cant even find that option in pro.
i know that this sounds stupid, but can anyone point me in the right direction?
thanks all!

This is how I have done it:
Export your 16:9 project as an .avi file.
Then import this file into a new 4:3 project.
It should automatically be letterboxed.

Or you could import your 16:9 project into a new 4:3 project.
I believe this should give the same result.

thanks for the reply.
for some reason though, it dosent work.
is there no "maintain aspect ratio" option?
thanks again!

There is an "interpret footage" option under the "file" menu.
In the project window, select the file you want to change, and then use the interpret footage to select the aspect ratio.