So, to help others who may want so tips, here is how I did it! First, find a picture, or draw one. I can't draw as well as a 4 year old, so I used google and printed off this pic.
Then I used some clear sheet (overhead projector sheets in this case) and traced around the bits of the image I wanted to use.
I wanted it to be a bit more 3d, so for my first tracing I ignored the legs on the far side, and for the 2nd I ignored the legs on the near side and filled in the gaps with my imagination. I was left with these two shapes which I cut out.
Now we are up to making the horse. I made marshmellow fondant - its awesome, you melt marshmallows and mix in icing sugar and hey presto fondant! Roll up a ball of fondant in your hand and then roll it out, mine was probably about 7mm thick.
Go and do likewise with the second shape.
At this point I make sure all the bits on the horse match and smooth away bumps that looks funny etc. Making sure that the front and back are joined so that you now have a horse with 4 legs and a hole through it.
We're up to the saddle! Colour a small piece of fondant to make the horse saddle. I used gel colours because they work great and don't melt the fondant. Roll it out thin - like 2mm and cut out your saddle shape. Mine is very plain but you can go crazy if you want to, you have my permission.
Arrange the mane piece on the horse, I still don't know the best way to do it, but you know, do what works, and when you like what you have, water/glue that toupee down. Next make a tail shape with the same colour as your mane, and cut a wedge out of Mr. Horse's bottom. Wet the pointy bit of the tail, and stick it into the wedge, squishing right in. In this case my tail was a bit long and I shortened it before sticking it in.