How do you make this kind of cow cake? I'm sure the butt/body was made using maybe the wilton ball pan (or soccer ball pan), but how do I make the head & legs? Do I just use pure fondant or cake or something else? I'm not that good at cake carving so hopefully it doesn't involve that.

This is the cake....

http://solidrecipe.com/wp-content/uploads/2011/10/Traceys-Cow-Cake-Photos-2.jpg

I don't think you have to carve much.  The body looks bigger than the Wilton ball pan.  You can use pyrex bowls to bake in.  The head looks to be near the size of the Wilton ball pan and carved a bit to get that shape.  The nose, legs and ears/horns look to be made of fondant.  You may need to carve the head a bit to get that shape but not much.   That's my advice if you don't want to carve much.  

Since the legs are laying flat on the cakeboard, weight shouldn't be an issue, I'd use fondant or gumpaste. If you want it lighter, rice crispy treats covered with foncant.

I would mix some white modeling chocolate with fondant. maybe 50:50...

if you have to cover such difficult areas like the legs or the neck with those small corners and cavities, it´s more forgiving. It doesn´t tear as easily and even if it tears, with the choclate in it you can fix cracks by warming the choclate-fondant-mixture with your fingertips and blend to pieces together. you won´t be able to tell that there were cracks at all. with pure fondant this might be harder to fix.

I made a snoopy cake that had a similar shape. with the modeling-choc mixed with fondant it wasn´t to hard to cover it.

hope that helps :)

AWe have half ball tins here, i'd use those.