You may need Tamiflu if you are on Holiday and contract H1N1, for treatment abroad you need a EHIC card.
Treament may mean a doctor or hospital or some medical professional prescribing Tamiflu after diagnosing you have the H1N1 flu virus.
In reality, at the time of writng this ( late July 2009 ) Spain, along with most European countries doe not have the stockpìles it needs for the population, but probably ( we do not know) has distributed existing stocks of Tamiflu to different regions including the Canary Islands, to Las Palmas and Santa Cruz.
The new, free European Health Insurance Card (EHIC card) is the card you will need to produce, however it is relatively new, replacing the E111 that existed before.
Most British people are not aware of this card, this means even less Spanish will be familiar with it, however most medical administrators will have a memo somewhere telling them about the change from 2006,
Chances are your EHIC card may be the first any medical worker has ever seen, be assured it will be accepted, you may have to insist though!