It's very likely you're correct, that the 30 days' notice clause would not be in effect until you actually started working. However, to be sure, I recommend you consult with an attorney. If you don't want to spend money on an attorney right now, you could wait until you receive a letter from the prospective employer's attorney and/or are served with court papers. It may well be this guy is just blowing smoke and won't actually follow through on his threats.

