Ok, slowly solving my own problems.
It seems that the directory for the sources is what I need. However, linuxmce does not include the sources anymore, [http://smart-home-blog.com/archives/1155]
I need to use the original ones from the vdr-project, which I downloaded here: [tp://ftp.cadsoft.de/]
However, now I got Problems with make. Running just 'make' on VDR tells me that fontconfig cannot be found, however apt tells me its version 2.4.2 which should be fine. Any ideas?
Sorry, if all this seems trivial, but it is quite an insight for me. Maybe for other newbies as well.