Just submit an initial application via the website. If you get selected then you have a period of time to complete the application and pay for your entry. Foreigners get some kudos and bigger groups get more chance too, so if you can find some buddies then that wil help. We got in with a group of about 8 brits in 2011.
Maratona is hard but not as tough as the marmotte. Maratone has more hills and the Giao is hard but the marmotte has more metres of climbing, and is longer. Watch the time cutoffs too – if you start at the back then you can’t hang about or they’ll stop you doing the long route (missing the Giao).
Great event though – very well run and a lovely area. Transport in/out is trickier than the marmotte though.