Thanks for the reply.
What I don't understand is why I need to do this. The first NIC is connect to a cable provided by my colo-host. This NIC has the 126.96.36.199 address and communicates true 188.8.131.52 (default gateway) with the rest of their net, and www. The other ip-addresses are not used right now, but I put 'em in ISPConfig anyway. Would it be wise to delete them in ISPConfig?
Tomorrow, I'll go back to create the virtual interfaces... but is anyone curious about some kind of output, please ask, so I can post the results tomorrow afternoon or night.