Warsaw to Vienna - tips?

I'd like to travel from Warsaw to Vienna (either by train or by bus) for a reasonable price, and I'm hoping some seasoned travel veteran (or just someone who has done it before, and successfully) would be able to provide me with some tips.

Where/how can one book bus/train tickets for a good price? Any tips on where to look?

(Any tips on what I should avoid, too, if you have any horror stories from which I can learn.?)

Thanks!

I would definitely recommend train, and on top of that, a sleeper. A few years back night trains from Warsaw were notorious for theft, but you'll probably be fine. I think now they have a police officer on each train, and the sleeping compartment cars are locked.

You don't need to be paranoid or anything, just be aware of whats going on