No problem.
1) Open new project and select video format in 16:9
2) Put your video in 4:3 on the video area
3) Apply the "zoom in" effect to all the video
4) modify the zoom effect: begin and end will be the start and the end of your video; zoom how much you need to have a 16:9 video format
Obviusly you will lose the top and the botton of your movie! but it's better than nothing! Ciao