According to the following install guide:
http://codex.buddypress.org/getting-started/before-installing/

How is it possible to setup my blogs to be directed via subdomains blog1.domain.de, blog2.domain.de instead of http://www.domain.de/wordpress ?

[@themightymo Participant 13 years, 10 months ago]

You need to set that up during the installation process. I believe it is very difficult to switch from a sub-folder setup to a sub-directory setup.

[@mercime Participant 13 years, 10 months ago]

@ddjjmm if you want your subsites/blogs to be directed to
blog1.domain.de
blog2.domain.de
blog3.domain.de
you must install WordPress at root, i.e. http://www.domain.de, and Create a Network with subdomain structure.