When I was in London recently I picked up a copy of Nigel Fosters Austrian Legal System and Laws, ISBN 1-85941-757-4
It cost £35 (amazon.de is offering it from 85.95 euros, which is worrying)
There is also Hausmaninger, The Austrian Legal System 3rd ed., ISBN 3-214-00289-9
I have only the first edition of Hausmaninger, dated 1998. That has less substantive law than Foster. But I don’t know if the later editions are fuller.
Maybe books on ‘smaller’ legal systems concentrate more on the framework. They expect you to know a lot about German-language civil law (and criminal law) from books about German law. That was the impression I got from a book on Canadian law, that it wanted to spare me the basics: Stephan Handschug, Einführung in das kanadische Recht, 2003, ISBN 3-406-50826-X – a lot about constitutional matters in there (perhaps the more so since the written constitution is relatively recent).