Failed to fetch 404 errors during apt-get commands

I am using Xenomai linux, and I have internet on it, but when I do apt-get update or apt-get install I get like this `http://security.debian.org/dists/etch/updates/contrib/source/Sources.gz 404 Not Found [IP: 212.211.132.250 80] ` I understand it has to do with unsupported repositories, but I googled around, but couldn't find what I need to do to fix it for Xenomai. This is my /etc/apt/sources.list: # # deb cdrom:[Debian GNU/Linux 4.0 r3 _Etch_ - Official i386 NETINST Binary-1 20080218-14:15]/ etch contrib main deb http://ftp.nl.debian.org/debian/ etch main deb-src http://ftp.nl.debian.org/debian/ etch main deb http://security.debian.org/ etch/updates main contrib deb-src http://security.debian.org/ etch/updates main contrib