deb
http://ftp.us.debian.org/debian unstable main contrib non-free
deb-src
http://ftp.us.debian.org/debian unstable main contrib non-free
These are the lines I would add to enable unstable sources with apt. BUT, I am unsure about doing this if you are trying to only upgrade a few certain packages to unstable.. Doing it this way I believe will upgrade EVERYTHING available...
However, I do know there is an apt-get switch that will allow you to install a certain package from stable/testing/unstable (what ever you choose). You do not have to have that particular one in your sources file either.
# apt-get -t distribution install package
Read more on section 3.8 at this link:
http://www.debian.org/doc/manuals/ap...pt-get.en.html