bad PCM?

I got a mailorder tune from Madz28 and I was trying to install it but was unsuccessful. I put the OBD1 PCM w/LT4 knock module in the car and when I tried to read the stock tune it would come up with "Incorrect Response from PCM." I bought the PCM off ebay. I tried to start the car with the OBD1 in there just to see what would happen and the car will start but will shut off immediately. I have also heard that when doing an OBD2 to OBD1 swap you need to switch the knock sensor in the block for one from an OBD1 car which I haven't done. So could I have gotten a bad PCM?

Yes if you convert from OBDII to OBDI you must change out the knock SENSOR to OBDI.
I'm pretty sure madz28 makes sure the PCM is ok before tuning on it. However I'm not sure if the incorrect KS would give you that error.
Try to put a OBDI KS in and see if that works.