What camera for ultra zoom and low light, deer pictures?

[jab862]

I need advice on what digital camera to buy. I want something that I can take hunting with me and get pictures of deer that I might see that would range in distance from 5 to 100yards and almost always in lower light conditions. I bought a Casio Exilim EX Z1000 thinking it was small and with the 10.1 mega pixels and the 3X optic zoom I could enlarger the pictures and get what I wanted. Well a deer in some what low light and at 15 yards looked more like a spec than a deer and when I went to digitally zoom in on it the clarity was terrible. It was not even close to viewing the deer with the naked eye and I was hoping for better than that.
I have been looking at cameras in the $400-500 range and have seen some with ultra zooms and even IR capabilities. I have IR game cameras but have no idea what an IR regular camera does. I don’t want to buy something and end up like I did on the Casio, no good for my application.
Any suggestions would be greatly appreciated.