Simulating a 2 Legged Kangaroo Robot Jumping - Where do I start?

I'm building a hydraulic powered kangaroo robot, and I would like to create a simulation of it making one complete jump. I have very little of an idea of where I should start. What other programs will I need (like simulink, or simmechanics), and which one should I begin with? Are there any resources I might be able to utilize that could help me get started? I understand this is a very open ended question, but any advice would be greatly appreciated.