Yes, BTC/EUR is available to trade. But BTC/EUR being available to trade is a different thing from there being volume in BTC/EUR. Initially volume will be low to non-existent until more users sign up and build up the market. As I said in another post, we'll be providing some liquidity for some pairs eventually, but for now it's up to users to create the market. Traders should pick their prices and stick with limit orders. Until the volume picks up, it's best to avoid market orders since they can fill at unfavorable prices when liquidity is low.