I will be arriving from Salzburg?

I am travelling from Salzburg to Rome via Vienna. I thought it maybe possible to visit to St Stephens's cathedral. Do I have to pass through customs/immigration as I will be arriving from Salzburg? I was wondering if anyone can tell me please if it is possible to take a day trip from Vienna International Airport to the city. I will appreciate all your suggestions. Thank you.

This is a web site about Japan, katrina. Perhaps you should visit www.lonelyplanet.com/thorntree instead.

From my experience I'd say that it all depends how your flights are scheduled.
The things is that you can go out and come back to the airport but you'll need to go through screening and checking again, which is pretty time consuming.