put both versions of the video onto one sequence/timeline.
Are both video clips the same thing, just different resolutions/frame rates?
the videos are differnt "things" but they are different resolutions and frame rates. I want to make this a widescreen (1.333) project, then somehow put some 4x3 footage into it (I'm aware that the 4x3 footage woulld have black bars on the left and right, that's okay. But the 1.333 footage I have is (as I said) 23 fps, and the 4x3 (0.9) footage I have is 29.97.
with CS4, that's no problem at all. Premiere Pro handles the frame sizes and frame rates.
Make sure you have the 'scale to frame size' preference set correctly and you should be good to go.
You might check out this tutorial that I did some time ago on this subject:
a widescreen (1.333) project
As a point of interest, 1.333 represents the aspect ratio of normal, squarish images (4 divided by 3), not widescreen. The widescreen aspect translates to 1.777.
The Pixel Aspect Ratio is .9 (roughly) for normal video, and 1.2 (roughly) for widescreen in the NTSC/ATSC system.