That would be beyond the realm of my experimentation with Zentyal. But when you consider everything in play then it's unlikely that your Zentyal box would just be able to replace your Windows one. I think that a clean start using a new domain will probably cause you less headaches. Do you have many users to migrate?
What you can do, as I did myself, is set up Zentyal in a VM and mess with it. I'm currently using that technique to prepare my 2.0 install. You could set up a second VM as a client computer so that you can disconnect your virtual network from your physical one and play around.