Only one Toyota Prius, the new 2010 Prius will be sold throughout Europe, the outgoing model will no longer be available there.
Toyota has made a decision and the decision is exactly the same one they made for the U.S. The will only export the new 2010 Prius and will not sell it side by side with the outgoing model.
It seems as though only the Japanese market will get the option of two Priuses. The benefit of selling two Priuses allows Toyota to price the outgoing model at a lower price than the new model and thus creating competition with the Honda Insight.
The decision by Toyota likely involves currency exchange rates that simply will not allow them to sell the old Prius at a discounted price and expect to still return a profit.
Another speculative commenter believes that Toyota is selling the old generation Prius in Japan to get rid of a stockpile of vehicles they still have left due to the economic downturn.