Thanx ggc for your reply.
I got it working just a few minutes ago, but it’s interesting what the problem was: I had a clean install of system and programs. As a late C6.5 adapter, I came into this grace period thing, where you get a slim lined installer (where parts of the sound library are missing because they are redundant to the ones on the 6.5 installer mediums).
C7 installed fine. Since I use mostly 3rd party sampler and stuff, I did not install the sounds, soundsets and samples from the C6.5 DVD.
This afternoon, I installed those files and there it was it: the Installer for C6.5 asked for Microsofts Framenetwork 2.x and 3.x. Those Microsoft extensions were missing on my system… - why on earth is it not possible to build in some test routine that gives out a warning like: please install MS Framebla?!
Anyway, problem solved