Mackenzie was the same from about 18 months and we are just consistant with the disipline. We have the naughty corner which she goes to if she doesn't say sorry for her actions. She is now 2 and understands what she is doing is wrong. I watch her when we are at play group etc as I can see when she is about to strike and I try and remove the situation before it happens but in saying that there are others there who also hit and bite and their parents just let them go. If they hit Mackenzie she usually 'fights' back (for the want of a better word) but I then remove her and explain that we still don't hit. It's tough on you too but I'm told by everyone that the biting will stop - and I think we are getting to the end of that now and it really is an age thing. Good luck and just be consistant.