What is the best way to get from Hallstatt to Vienna by train?
You can look at the schedules at http://reiseauskunft.bahn.de/bin/query.exe/en?country=USA
Looks like there is a connection every 2 hours that will get you to Vienna in 3 1/2 hours with a single train change.
blew,
As Sam mentioned, it's quite straight forward. Hallstatt is somewhat on a "spur line", so at least one change at Attnang-Pucheim is often required (depending on which train you choose).