there is only one currency in Greese - Euro.
Normally nobody would sell you anyting for USD in the Europe.
As for now Greece is located there.
My tip: take some small sum in Euro e.g. 20- 30 Euro,
normally for some absolutelly unnesessaRY tourist stuff they would
accept your credit card (Visa, masterkard).
And don't hope to see something interesting in Greece - that is really one of the most
boring country in the word : all interesting stuff about Greese one can read in wikipedia.