Re: Sightseeing tips in Vienna?... It depends what you like, but I am assuming that you are a big fan of music
Seriously, dress up and visit the Bosendorfer factory/showroom, a 10 minute walk from the Opera house. Play on an Imperial Grand and let us know what you think?...
A sentimental favorite of mine was visiting the National Cemetery (Zentralfriedhof) where you'll discover the graves of Beethoven, Brahms, Schubert, Strauss (father & son), and a monument to Mozart. It's a 30 minute bus ride from the inner city. From the main entrance, you'll walk through beautiful gardens before you're in midst of the Greats. I think that it's a pilgrimage that every musician should make in one's lifetime. Last time I was there, I placed some flowers over Beethoven's grave. Prepare yourself, because I didn't. For me it was very emotional; it was as if I had journeyed to the Earth's core - the energy was surreal. As I gazed over the monument for the first time, the opening bars of the Eroica Symphony kept resonating in my head, then I calmed down to to the elegiac 2nd movement of the Pathetique. A sublime experience, and I can promise that you'll never play Beethoven the same way either.
The Opera House, Hofburg Complex, St. Stephan's Cathedral, Schonnbrun Palace, and the Musikverein are also very good sites. Don't forget to sample the pastry too!
I was there in Vienna and Salzburg for Mozart's 250Th anniversary and the summer music festivals 2 years ago. I do a lot of landscape photography on my trips, and for me it was a musical and photographic safari all in one.
Will you be touring outside of Vienna too?....
Lastly, buy a DK Eyewitness Travel Guide on Austria or Vienna - Best $20 you'll ever spend for any European trip as it is an exquisite compact guide - pictures, descriptions, maps, schedules, history, etc.