to book or not to book??

[Terpe]

but its one of the requirements and we are afraid that if we dont book a flight it might affect to the decision of approving the visa :/

In principle you are correct, you need to book some kind of travel. You may also need to have some kind of travel insurance and an invitation letter from an Austrian resident.

Here is a typical Schengen Visa application form :-
http://www.auswaertiges-amt.de/cae/s...antragEngl.pdf

May I suggest to contact the embassy/consulate just to be sure you will be able to comply with all requirements.