Hi Bastian
Kindly Refer the SAP links & Note 1676665 - Setting up Microsoft SQL Server 2012
Installation of MS SQL 2012 link - http://blogs.msdn.com/b/saponsqlserver/archive/2012/08/09/sql-server-2012-installing-sap-systems-based-on-sap-netweaver-7-31.aspx
Require SAP S-user id
MS SQL installation Steps
http://scn.sap.com/community/sqlserver/blog
Regards
Ram