You have two options here, first being to buy some type of trailer either enclosed or open. Or second to get a hitch mounted carrier, do a google search for this. Its pretty much just a bar running parrel with your bumber of your car that your dirtbikes stands on, there is no axels. This is great for long trips because you does have to pay extra at tolls but you do not get extra storage that a trailor provdes.
But for either of theres alternatives you still need a hitch, I belive uhual can put one on for you.
Also, I learned this the hard way, lock your bike to the trailor and lock the trailor to the car!!!!!!