In Austria where do I by a highway permit (7,60 per ten days)?
If you're looking for the Vignette you should buy it before you get to Austria. Any petrol stations on the way will sell them.
Oh, and although it probably doesn't apply to you, it's illegal to have more than 2 vignette stickers on your windscreen at any given time. Sure you see people with lots of them but they can get pulled over.