What you have calculated is the probability that, if you flip two coins, a penny and a coin made in 2008, one or both of them will come up heads. This is analogous to the sprinkler/rain problem - the grass can be wet by either or both of two independent events.

I'm not sure if there is a way to find P(heads | 2008 and penny) using only the information given, but I don't think a computer program would be confused by this kind of thing if it kept rigorous track of the events that its probabilities refer to.