The most comprehensive information for foreigners is to be found on websites in German. If you are not yet fluent in German, try to find a native speaker to help you. It is also a good strategy to get someone living in Austria to call up the relevant institutions for advice if something is not clear or you have a special case. In many cases, using a specialist lawyer to assist in your application may increase your chances of a successful application.
Arbeiterkammer Österreich
http://www.arbeiterkammer.at/www-3071.html
This is the official institution for all employment issues in Austria. The site is in German and contains very useful information on work permits and related issues. You can also call them up and they will help you.
City of Vienna
http://www.wien.gv.at/fremde/aufenthalt/titel.htm
As the capital of Austria, Vienna hosts all offices and institutions you will need to contact during the application process. The Vienna website offers a good overview of the process steps and requirements and you can also download most forms there.