I don't believe you can. I haven't seen a function for this anywhere in
VideoFactory. But if you're serious about sound editing, SonicFoundry
has pretty much the best tools available. Sound Forge XP Studio 5.0
has just about everything you could ever think of doing to sound files:
dozens of effects, load/save mulitple formats, mp3 encoding/decoding,
rip from CD, time stretch, pitch bend, dynamics, eq, and .... reverse. It's
only about $60 for the download. Of course, you can download it and
try it for free. (ok, ok, ok ... i know, i sound like an advertisement for SF.
sorry!) I also have the full version of Sound Forge 5.0 which has an
incredible assortment of tools, but that is $350 for the download and is
probably extreme overkill for a small video editing studio.

On the other hand, if you just want to reverse some .wav files for free,
Windows includes a program called Sound Recorder, under Start,
Programs, Accessories, Entertainment. This utility lets you do some
basic cropping and format conversion, as well as reverse and echo.