Since the two sets of dimensions are not the same ratio, you will probably have visual issues, with things looking squashed, possibly making some text less legible. You could also have a problem if your professor doesn't buy into this approach to a solution.
Then what I can do?? The only solutions I know is to resize the .swf like this or leave the resolution at 1024x768.
Resize everything into the .fla file would be so boring...
Edit: I've checked every text field and it looks good; everything is good so I didn't tought at a problem but you might be right: my professor could not enjoy my resize solution.
Select everything on every layer and with the "edit multiple frames" option turned on, scale your content proportionately to 800x600. Don't forget to select everything on the scene before scaling, just checking "edit multiple frames" wouldn't be enough