Unless you have a really sweet machine (and even then, it's not recommended), you shouldn't be deinterlacing in real-time. The only advice I can give on the audio is to check the "volume meter" under VDub audio options and make sure the VUmeter is showing something during your preview. Sometimes, I've accidentally had the mixer control set to the dedicated mic-in instead of analog-in. Also, if you have the kind of capture card that has an audio input (some of them are only mono, actually), you might try just going directly into the soundcard instead.