The difference in speed between 30 FPS and 29.97 is negligible (.1%), the conversion process only involves changing the header to play it back at one vs the other. As mentioned you should be able to accomplish this in Virtual Dub, though there are many other ways to go. Overall though, even the best videophiles I know can't discern the difference between 30 and 29.97.
If you want to talk bad frame rate conversions, in some PAL environments they will take 24FPS Movies and speed them up to 25FPS (4%) rather than display a frame twice. Generally the audio needs to be handled a little more carefully to prevent high pitched voices from the speedup. Still most people do not notice this difference although It is in fact really annoying for some.