Please write an email to felix.friedrich (add an at here) inf.ethz.ch when you need write access to the repository. If you are an external user (i.e. you do not have an ETH-login), you may want to register first as described on the following page http://www.isg.inf.ethz.ch/ServicesVersionControlAccess.
Read-access for the trunk is already granted for anonymous users. Read access to other parts of the repository require special permissions as for the write access. Use
svn checkout https://svn.inf.ethz.ch/svn/lecturers/a2/trunk a2
to checkout the repository. If you experience problems checking out without username, please register at http://www.isg.inf.ethz.ch/ServicesVersionControlAccess and send an email to felix.friedrich (add an at here) inf.ethz.ch.
For some environments, anonymous user does not work. There is a special user for this case : eth.a2guest:a2guest.