Raisola,
This topic has apperaered in the past here on the HUBB so many of your questions might be answered by a bit of a search.
From personal experience of having done the buy and sell route I can tell you several things.
The European Union countries have some strict rules on buying used bikes or cars and you can get them registered in your own name only if you can demonstrate your status as a resident of that country.Some countries apply them very stringently - like the Netehrlands - and it will be a practical imposibility to buy and get a bike registered in your own name there. I have read here on the HUBB that in England this is not a problem . Germany too may be a bit more flexible.
The way around this is , and this was suggested also by an offical at the Dutch registration department,RDW, is to have the vehicle registered in the name of some other person who does live in the country . This will only be possible if you are well aquainted with one of the locals who would then be willing to accept the responsibility and risk of letting you galavant around on what will be technically his bike- and HE will get notice of any tickets you rack up from photo radar etc.
I have used this method repeatedly on visits to the Netherlands where I have connections who will let me register the bike for me which I then use for about 3 months of touring around all Europe and on the last trip even into Morocco.
If you have or can establish such a relationship with somebody in Europe it can save you much money if you buy a recent model bike . Another plus is that you may get all the liability insurance you need , "the green card" simply and inexpensively by being written in as a second rider permitted to operate the bike on the insurance policy of the registered owner(of course you pay for the additional charge and a pro rated amount for the time you are riding).
You will of course be faced with the expense of buying a fairly recent reliable used bike and selling it at a loss at the end . For only a two week trip you must do some serious calculating with respect to advantage over rental. Perhaps you can talk a dealer into renting or "selling" you a used bike but keeping it registered under the shop name, you pay for all insurance and post some sort of surety bond to cover any eventual tickets/fines you may get sent to his address. The final sum can then be regulated in the end when you sell the bike back to him.
How about some replies from the various EU countries on the specific restrictions in your corner of the continent.

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http://advrider.com/index.php?thread....207964/page-5 then scroll down to post #93