"An alternative when you do not want to do as much on your brother's computer
and do have a Linux system yourself, is to just forward all IPIP traffic received by your brother's computer to your computer over the local network, and run ampr-ripd etc on your own computer. "
This is exactly what I want to do but I have no Idea how to do it. By "all IPIP traffic" do you mean _only_ the IP Protocol 4 Traffic or do you mean effectivly all IP traffic (I dont think that would be ok.)? I ask this because my brothers computer has several websites and a few other web services (IRC, SSH, FTP, Minecraft) running on it and everything that I do cannot interfere with them.