In case you can't install Parallels Tools:
Add the needed resources first:
Add the needed resources first:
/etc/apt/sources.list
just add:
deb http://ftp.de.debian.org/debian/ stable main contrib non-free
deb-src http://ftp.de.debian.org/debian/ stable main contrib non-free
deb http://security.debian.org/ stable/updates main contrib non-free
deb-src http://security.debian.org/ stable/updates main contrib non-free