Old Toad is right. Run the firmware update and update the target display to make sure everything is up to date.
You can connect MDP to MDP - obviously...
You can connect TB to MDP.
You can connect TB to TB - obviously...
You cannot connect MDP to TB.
This Apple web page says that it is possible! Go down to point five! Then you will be able to see what you need to buy to do it correctly.
That should be all you need! Good luck! Let us know what you buy or if you want some advice on what to buy!