Rule 1 of the Mongol Rally: Small and crap. Your car needs to be under 1.2L, or 125cc if it's a bike.
To ship your car, your vehicle must be registered in the EU, it must be registered in the name of a team member and it must fit within these dimensions Length - 470cm, Width - 215cm, Height - 190cm and Weight - 1500kg.
You've already got a car outside the EU? Read this
If in any doubt, email email@example.com.