I worked briefly for a company that has since gone into bankruptcy. Over 2 yrs later, I got a W2 from them. Do I have to file an amended return? Am I responsible for the late penalties?

If in fact you did not include this income on your 2007 return then yes - you should file a 1040X to correct this. I have to wonder how you didn't notice that you were missing a W2 when you filed your 2007 return. As for penalties - are you sure that by reporting this you will owe any money to the IRS? This new W2 should show taxes that were withheld at the time, so perhaps you actually have a refund coming. However, if you do owe back taxes (and interest on late payment) then you will just have to pay it. You're certainly not going to get any money out of a company that has gone bankrupt.