There are strong differences in Austrian and German vocabulary, but as far as an actual Austrian accent, its hard to say. In Germany itself there are at least 30 different sub-accents, and Austrian German has 3 or 4 major groupings of dialects with several more under that.
To put it simply, though, in Vienna the accent spoken is a little bit more nasal, and there is what you might call a "Drawl", in which vowels are extended with a diphthong, and certain vowels (especially i's and e's) are transformed into o's and ah's.
Its really hard to describe without a basic knowledge of German, but you can think of the Viennese accent as similar to the Southern U.S. dialect (which I speak) in that the pronunciation is a little more relaxed than High German, and in that there are non-german influences (obviously such as Hungarian and Czech).
So, be german, but more nasally?