Maintaining 4:3 aspect ratio?

[Tristan Horn]

Pardon me if this has been asked before, but I'm new and the list archives
aren't available...

I've successfully transcoded three basic quality shows to DivX 4 (using nc,
sendstream, Elecard's decoder, Avisynth and VirtualDub).

I chose to resize to 704x480 (352*2=704). I'm fairly sure that this is
stretching the video too much, so I'm going to start using 640x480.

The question is: should I resize to 640x480 before or after cropping out
the green bar?

thanks,
Tris