You need to add two words in your /etc/apt/sources.list file. Those words are, non-free and contrib. Open /etc/apt/sources as root.

Find the following lines:

deb http://ftp.debian.org/debian/ etch main
deb-src http://ftp.debian.org/debian/ etch main

and make them look like this:

deb http://ftp.debian.org/debian/ etch main non-free contrib
deb-src http://ftp.debian.org/debian/ etch main non-free contrib

You may also want to add contrib to your security updates if it isn’t already.

deb http://security.debian.org/ etch/updates main contrib
deb-src http://security.debian.org/ etch/updates main contrib

In order for apt to understand the new changes we must update it:

apt-get update

Install the package with:

apt-get install msttcorefonts