There are alot of things that come in to play when trying to get good wildlife photos, amount of light, zoom level, appeture speed, ISO settings, how stable the camera is, ect... A digital SLR type camera is the only way to go for very good photos
Optical zoom is definetly the way to go, it provides the most clearity, a digital zoom will act in the same way as zoom in on a picture that you are editing after it is already zoomed to full size, it distorts the image in order to enlarge it.
I have had alot of experience with the Panasonic Lumix DMC-FZ series of digital cameras and these are some of the best units on the market for their price. 10X optical zoom, image stabilization, a good array of manual settings, ect..
This photo of a nice Ohio buck was taken with a Panasonic Lumix DMC-FZ5 which is a older unit, it was taken at a distance of around 100 yards in very low light conditions....
