Installing R on Debian testing...

Hello!
I have posted this question at the R-HELP, general.

I recently switched to Debian testing OS and explanation at the:
http://cran.at.r-project.org/bin/linux/debian/
is a little bit fuzzy. Can anyone give step-by-step how-to have updated
R on Debian testing and/or unstable.
First, what line should be in /etc/apt/source.list?
Second, how to "approach" to unstable versions?

Thanks in advance!
PM