Tough Mudder - 12 Mile Assult Course

http://toughmudder.co.uk/about/

I'll be taking part in this in October, I've got 6 months to train up.

I'm wondering if anyone would be able to give me advice on how I should train for this.
I'm not in great physical shape, but I'm extremely deterimed.

I'm 18 - 5'5" & about 68 kg.