There's only 2 options:
1) stretch the image to 16:9. Many monitors and DVD players can do this using various stretching techniques. Some of them are watchable, if they use a variable stretch algorhythm. None of them require you to do anything with the image. Using a video editor to stretch it can be done, but the results are pretty poor, as they will use a constant stretch rate.
2) Crop the image to a 16:9 ratio. This was recently covered in another thread. The results will be very poor. 4:3 images are at a max resolution of 640x480. In order to make it 16:9, you would crop the top and bottom till you had something like 640x360. The resulting image, when displayed on anything larger than a 30" 16:9 monitor would be pretty poor. This is due to a 360 res being stretched back to 480. (16:9 at 480i is 720x480)
You could apply some combination of the 2, stretching and cropping, but you'd still be stretching a limited number of pixels into a larger area.