i dunno, to me, guilt is just that internalized parental figure, or the angel on your shoulder, if you like. it scolds you for breaking a rule, or not fulfilling a duty. empathy, like someone else already put it, is putting yourself in someone else's shoes. the two could definitely overlap, but i don't think that makes them the same thing.
that is to say, you could react to that same scenario three different ways. a) empathy, no guilt
"Man, it must be so difficult to get around in that condition. I know I'd want help if I was her. But I didn't see it in time, so there's nothing I could have really done. Oh well."
b) guilt, no empathy
"I should have helped that woman on the bus. Damnit. Though I don't see why it should necessarily be me, or why anyone should need so much help. But still, the fact is, I didn't do my duty."
c) both (as in how you reacted, no need to restate it)