If VirtualDub's internal IVTC is leaving some interlacing artifacts, you could try Donald Graft's "Decomb" filter for AVISynth - I've had much more luck with it.

For me at least, interlacing artifacts can spoil an otherwise outstanding transfer (in the TR47 versions, see the brief lightsaber glitch just before Luke drives Vader off the carbon-freezing level in ESB or the more obvious full frame combing for a second when the Emperor is frying Luke in ROTJ), so it's important to find a setting(s) that works and to check the whole final product for errors. Please keep up the good work, MeBeJedi!