I did not know, regardless of possibly 2010, that it will happen that "soon". Do you have any information about possible designs of their coins?
That's only the earliest date and only if the language of the agreement can be spelled out before June 2009. It is possible that this could happen by then, but it is not probable.
I've seen the proposals for designs- most of them have Charlemagne as the main design theme. None of them can be approved until at least an 'agreement of principle' is worked out.
When this happens, the agreement will be unique among the Eurozone members. Since Andorra had no pre-existing arrangement with either France or Spain (as San Marino and Vatican City did with Italy or Monaco with France), they will have to sort of merge with only a portion of the EU.
The parts of the agreement that are rocky at the moment involve euro introduction as a path to EU membership. Andorra would have to join the EU once they adopt the euro.