The main reason I used GoldWave in the past was the batch mode. TMPGEnc would be finicky about videos with some types of audio(for instance .ac3 it did not at all if you didn't buy the extra plugin.) With GoldWave you can open the batch window and drag & drop a bunch of .avi files and it will output .wav files with the same basenames(or .mp3 or other supported audio type, but I used .wav for TMPGEnc.)
I don't use TMPGEnc much anymore. But for free I figured I'd install GoldWave and check it out after all this time. It installs and comes up in Vista64 so I'm assuming it works on 64 bit.
