What's the best way to get from Vienna airport to the city center? We arrive in the morning (around 6.30am) and would like to leave our bags at our hotel -- the K+K Maria Theresia -- even if our rooms are not ready.

How much would a taxi cost? Or the train/metro? (In which case, would we need to take a taxi from a central station?)

Thanks!

A taxi should cost you somewhere in the 30 to 35€ range...earlier this year I paid 32 € for a taxi to the Hotel Viennart which is close to your hotel. I booked the taxi at one of the reservations desks in the arrivals area...they're very clearly marked and visible.
Vienna doesn't have a central station. For example, there's the Westbahnhof (which also is not far from your hotel, although I wouldn't want to walk it after a long flight) and the Sudbahnhof (which is not close to your hotel). There's a bus from the airport to the Westbahnhof.
This link will give you info on the various transport options:
http://tinyurl.com/2m8dgg

Forgot to add, you should like the hotel, it's a very nice one. Fingers crossed, maybe they'll give you one of the rooms with private roof terraces.

Combine with BTilke's link the hotel's own directions: http://www.kkhotels.com/index.asp?ID=372#Hauptbereich

There are two rail services from the airport. Both are fine, so use the cheaper one unless you really need to save ten minutes. Last year the price was €3 or thereabouts.

there is also a shared van service that is cheaper than a taxi. it also can be booked at the airport. i saw signs on my way down to the train.

if you do take the train.. be sure to get a day pass for the city ( so you can hop on the trams at will)PLUS the supplement ticket for the section from the airport to the edge of city zone.

Take the CAT train from the airport to the City Airport Terminal (hence the name), a 15-minute ride for 16E return. From there follow the signs to the U-Bahn.

Thanks for the information! We'll probably use the City Airport Train and then the U-bahn.

The CAT costs far more than the U-bahn for the same journey.

Padraig,
I think you mean the S-bahn from the airport. You are absolutely right though, it is much cheaper that the CAT and does not take that much more time to get to Wien Mitte station for transfers to the U-bahn.