Well in most legal cases, your example would be considered manslaughter due to lack of mens reas (intention to commit a crime; in this case "to kill") as opposed to say Murder, thus carrying a different sentence (manslaughter carrying a more lenient one)
I'm pretty sure it's a similar case in Islam, but I'll look up manslaughter (in my trusty sharia law handbook) later on today and get back to you.
EDIT:
Regarding Manslaughter (unintentional/accidental killing), it says to pay Diyah or Blood money to the deceased's family.
For a more detailed answer, please check:
http://islamqa.info/en/ref/52809
I will make a thread regarding application of Hadd punishments soon as there's a lot of valuable information and insight that I think is worth sharing.
For the umpteenth time, please also consider purchasing this book:
http://www.islamicbookstore.com/b2440.html if you haven't already done so. Yes it's a little expensive, but this is definitely a must have for Muslims and Non-Muslims who wish to learn more about Sharia law. I cannot recommend it enough - purchased it well over 4 years ago and I still learn new things each and every time I read it.