I'm hoping to go to Vienna this year, as well. I want to join in the celebrations for Mozart's 250th birthday. There will be loads of music to hear, but I can't go until later in the year as I am not allowed to fly just yet.
Last time I was there I went to the volksoper. You can normally get tickets quite easily - we booked up only two days in advance of the performance. Saw Hansel & Gretel and it was absolutely wonderful - a marvellous atmosphere.
Hope you enjoy yourself as much as I did Janexxx.