This is not something that I have any background expeirience on, but I did do a bit of surfing on the net.
It appears that you are not liable. The credit card company will try and collect from the estate, but if no money was left then they can not collect. If the estate doesn't pay, then the amount will be written off against his name.
Here is some information that may be of help <A HREF="http://www.faqfarm.com/Credit/Card/1309">Who is responsible for your credit card debt after you die?</">