Am going through this EXACT same thing right now, Isaiah (our now 82 pound boxer boy) ate a whole flippin pound of a chocolate easter rabbit last night. I called the ER vet and talked to some friends of mine that are vet techs and thank God that he's a fatty boy right now, if he was any lighter in weight, it would have been a toxic level for him. Here's a link my friend sent to me last night that tells about the ammounts of toxidity, hope it helps and I hope your baby is ok:
http://www.petplace.com/dogs/chocola...ity/page1.aspx